Picture decoding device, picture decoding method, and picture decoding program

ABSTRACT

There is provided a picture coding device that performs intra prediction coding of a picture signal including a luma signal and a chroma signal in units of blocks and codes information relating to an intra prediction mode. When the intra prediction of a picture signal is made in units of coding blocks, in a case where a chroma format is 4:2:2, in a mode for setting a chroma intra prediction mode in accordance with the luma intra prediction mode, an intra prediction unit sets the chroma intra prediction mode based on the luma intra prediction mode and the chroma format and makes an intra prediction of the chroma signal.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.14/860,246, filed Sep. 21, 2015, which is a Continuation of U.S. patentapplication Ser. No. 14/490,286, filed Sep. 18, 2014, which is aContinuation of U.S. patent application Ser. No. 14/132,423, filed Dec.18, 2013, which is a Continuation of PCT International Application No.PCT/JP2012/003879, filed Jun. 14, 2012, which claims the benefit ofJapanese Patent Application Nos. 2011-136641 and 2011-136642, filed Jun.20, 2011, all of which are incorporated by reference in their entirety.

BACKGROUND

The present invention relates to a picture coding and decodingtechnology, and more particularly, to an intra coding and decodingtechnology.

As a representative compression coding mode of moving pictures, there isan MPEG-4 AVC/H.264 standard. According to MPEG-4 AVC/H.264, coding isperformed in units of macroblocks acquired by partitioning a pictureinto a plurality of rectangular blocks. The size of the macroblock isdefined as 16×16 pixels in a luma signal regardless of the picture size.While a chroma signal is also included in the macroblock, the size ofthe chroma signal included in the macroblock differs in accordance witha chroma format of a picture to be coded. Thus, in a case where thechroma format is 4:2:0, the size of the chroma signal is 8×8 pixels, ina case where the chroma format is 4:2:2, the size of the chroma signalis 8×16 pixels, and, in a case where the chroma format is 4:4:4, thesize of the chroma signal is 16×16 pixels.

As the chroma format, the ratio of sampled pixel numbers of threesignals of one luma information unit and two chroma information units isdenoted by X:Y:Z. As the chroma formats of a picture that is a targetfor being coded and decoded in accordance with MPEG-4 AVC/H.264, thereare 4:2:0, 4:2:2, 4:4:4, and monochrome.

FIGS. 3A to 3E are diagrams that illustrate the chroma formats of apicture. In the figures, “x” denotes the position of a pixel of a lumasignal on the plane of the screen, and “◯” denotes the position of apixel of a chroma signal.

The chroma format of 4:2:0 illustrated in FIG. 3A is a chroma format inwhich chroma signals are sampled in both horizontal and verticaldirections at a half density with respect to luma signals. In addition,in the chroma format of 4:2:0, chroma signals may be sampled atpositions illustrated in FIG. 3E.

The chroma format of 4:2:2 illustrated in FIG. 3B is a chroma format inwhich chroma signals are sampled in the horizontal direction at a halfdensity, and in the vertical direction at the same density with respectto luma signals.

The chroma format of 4:4:4 illustrated in FIG. 3C is a chroma format inwhich chroma signals and luma signals are sampled at the same density.

The chroma format of monochrome illustrated in FIG. 3D is a chromaformat that is configured only by luma signals without any chromasignal.

While the luma signals and the chroma signals are set so as to sharecoding information such as motion compensation and are coded anddecoded, in the chroma format of 4:4:4, a structure is also provided inwhich one luma signal and two chroma signals are independently coded anddecoded as three monochrome signals.

In the AVC/H.264 mode, a technique is used in which a prediction is madebased on coded/decoded blocks within the coding/decoding target pixel.Such a technique is called an intra prediction. In addition, motioncompensation is used in which a coded/decoded picture is set as areference picture, and a motion from the reference picture is predicted.A technique for predicting a motion based on the motion compensation iscalled an inter prediction.

First, in an intra prediction made in intra coding according to theAVC/H.264 mode, units in which switching between intra prediction modesis performed will be described. FIGS. 4A to 4C are diagrams thatillustrate the units in which switching between intra prediction modesis performed. In intra coding according to the AVC/H.264 mode, as theunits in which switching between intra prediction modes is performed,three types including a “4×4 intra prediction”, a “16×16 intraprediction”, and an “8×8 intra prediction” are prepared.

In the “4×4 intra prediction”, luma signals of a macroblock (a lumasignal 16×16 pixel block and a chroma signal 8×8 pixel block) arepartitioned into 16 4×4 pixel blocks, a mode is selected from among 9types of 4×4 intra prediction modes in units of the partitioned 4×4pixels, and intra predictions are sequentially made (FIG. 4A).

In the “16×16 intra prediction”, a mode is selected from among 4 typesof 16×16 intra prediction modes in units of 16×16 pixel blocks of lumasignals, and intra predictions are made (FIG. 4B).

In the “8×8 intra prediction”, luma signals of a macroblock arepartitioned into 4 8×8 pixel blocks, a mode is selected from among 9types of 8×8 intra prediction modes in units of the partitioned 8×8pixels, and intra predictions are sequentially made (FIG. 4C).

In addition, in intra predictions of chroma signals, in a case where thechroma format is 4:2:0 or 4:2:2, a mode is selected from among 4 typesof intra prediction modes of chroma signals in units of macroblocks, andthe intra predictions are made.

In a case where a 16×16 intra prediction is selected, the intraprediction mode of a luma signal is coded as one mode of a syntaxelement mb_type representing the type of a macroblock, and an intraprediction mode of a chroma signal is separately coded. In a case wherea 4×4 intra prediction is selected, after intra prediction modes of 16luma signals are consecutively coded, an intra prediction mode of achroma signal is coded.

In a case where an 8×8 intra prediction is selected, after intraprediction modes of four luma signals are consecutively coded, an intraprediction mode of a chroma signal is coded.

Next, units in which an inter prediction is made in inter codingaccording to the AVC/H.264 mode will be described. FIGS. 5A to 5H arediagrams that illustrate macroblock partitions and sub-macroblockpartitions. Here, for the simplification of description, only pixelblocks of luma signals are illustrated. In the MPEG series, a macroblockis defined as a square area. Generally, in the MPEG series including theAVC/H. 264 mode, a block that is defined as 16×16 pixels (16 horizontalpixels and 16 vertical pixels) is called a macroblock. In addition, inthe AVC/H.264 mode, a block that is defined as 8×8 pixels is called asub-macroblock. A macroblock partition represents a small block acquiredby further partitioning the macroblock for a motion compensationprediction. A sub-macroblock partition represents a small block acquiredby further partitioning the sub-macroblock for a motion compensationprediction.

FIG. 5A is a diagram illustrating that a macroblock is configured by onemacroblock partition that is configured by luma signals of 16×16 pixelsand two chroma signals corresponding thereto. Here, such a configurationwill be referred to as a macroblock type of a 16×16 mode.

FIG. 5B is a diagram illustrating that a macroblock is configured by twomacroblock partitions each being configured by luma signals of 16×8pixels (horizontal 16 pixels and vertical 8 pixels) and two chromasignals corresponding thereto. These two macroblock partitions arevertically aligned. Here, such a configuration will be referred to as amacroblock type of a 16×8 mode.

FIG. 5C is a diagram illustrating that a macroblock is configured by twomacroblock partitions each being configured by luma signals of 8×16pixels (horizontal 8 pixels and vertical 16 pixels) and two chromasignals corresponding thereto. These two macroblock partitions arehorizontally aligned. Here, such a configuration will be referred to asa macroblock type of an 8×16 mode.

FIG. 5D is a diagram illustrating that a macroblock is configured byfour macroblock partitions each being configured by luma signals of 8×8pixels and two chroma signals corresponding thereto. Each two of thesefour macroblock partitions are aligned vertically and horizontally.Here, such a configuration will be referred to as a macroblock type ofan 8×8 mode.

FIG. 5E is a diagram illustrating that a sub-macroblock is configured byone sub-macroblock partition that is configured by luma signals of 8×8pixels and two chroma signals corresponding thereto. Here, such aconfiguration will be referred to as a sub-macroblock type of the 8×8mode.

FIG. 5F is a diagram illustrating that a sub-macroblock is configured bytwo sub-macroblock partitions each being configured by luma signals of8×4 pixels (horizontal 8 pixels and vertical 4 pixels) and two chromasignals corresponding thereto. These two sub-macroblock partitions arevertically aligned. Here, such a configuration will be referred to as asub-macroblock type of an 8×4 mode.

FIG. 5G is a diagram illustrating that a sub-macroblock is configured bytwo sub-macroblock partitions each being configured by luma signals of4×8 pixels (horizontal 4 pixels and vertical 8 pixels) and two chromasignals corresponding thereto. These two sub-macroblock partitions arehorizontally aligned. Here, such a configuration will be referred to asa sub-macroblock type of a 4×8 mode.

FIG. 5H is a diagram illustrating that a sub-macroblock is configured byfour sub-macroblock partitions each being configured by luma signals of4×4 pixels and two chroma signals corresponding thereto. Each two ofthese four sub-macroblock partitions are aligned vertically andhorizontally. Here, such a configuration will be referred to as asub-macroblock type of a 4×4 mode.

In the AVC/H.264 coding mode, a structure is employed in which any oneof the above-described motion compensation block sizes can be selectedand used. First, as the motion compensation block size in the unit of amacroblock, any one of macroblock types of the 16×16, 16×8, 8×16, and8×8 modes may be selected. In a case where the macroblock type of the8×8 mode is selected, as the motion compensation block size in the unitof a sub-macroblock, any one of the sub-macroblock types of the 8×8,8×4, 4×8, and 4×4 modes may be selected.

Non-Patent Document 1: ISO/IEC 14496-10 Information technology—Coding ofaudio-visual objects—Part 10: Advanced Video Coding is an example ofrelated art.

When information relating to the intra prediction mode of a picturesignal is to be coded, information relating to the intra prediction modeof a luma signal and information relating to the intra prediction modeof a chroma signal are coded and are arranged within a bitstream.However, at that time, in a case where the arrangement is not incorrespondence with the chroma format, the processing efficiency may bedegraded.

SUMMARY

The present invention is contrived in consideration of such situations,and an object thereof is to provide a picture coding and decodingtechnology capable of coding a picture signal with high efficiency byperforming intra predictions of a luma signal and a chroma signal inaccordance with the chroma format.

In order to solve the above problem, according to an aspect of thepresent invention, there is provided a picture coding device thatperforms intra prediction coding of a picture signal including a lumasignal and a chroma signal in units of blocks and codes informationrelating to an intra prediction mode. The picture coding deviceincludes: an intra prediction unit (103) that, when an intra predictionof the picture signal is made in units of minimal coding blocks set inadvance, in a case where a partition mode in which the luma signal ispartitioned horizontally and vertically is set, makes an intraprediction of the chroma signal in units of prediction blocks of theintra prediction of the chroma signal within the minimal coding blockset in accordance with a chroma format; and a bitstream constructingunit (113) that constructs a bitstream in which information relating toa luma intra prediction mode of the prediction block of the luma signaland information relating to a chroma intra prediction mode of theprediction block of the chroma signal located at a reference positionthat is the same as the position of the prediction block of the lumasignal are continuous.

According to another aspect of the present invention, there is alsoprovided a picture coding device that performs intra prediction codingof a picture signal including a luma signal and a chroma signal in unitsof blocks and codes information relating to an intra prediction mode,and the picture coding device includes: a luma signal intra predictionunit (103) that, when an intra prediction of the picture signal is madein units of minimal coding blocks set in advance, in a case where apartition mode in which the luma signal is partitioned horizontally andvertically is set, sets prediction blocks of first to fourth lumasignals acquired by partitioning the luma signal of the minimal codingblock horizontally and vertically and predicts a luma signal based onneighboring blocks of coded luma signals in accordance with a luma intraprediction mode for each prediction block of the luma signal; a chromasignal intra prediction unit (103) that, in a case where the partitionmode is set, and a chroma format is 4:2:0, sets a prediction block ofthe chroma signal without partitioning the chroma signal of the minimalcoding block and predicts a chroma signal based on neighboring blocks ofcoded chroma signals in accordance with a chroma intra prediction mode;and a bitstream constructing unit (113) that constructs a bitstream inwhich information relating to the prediction modes is arranged in orderof, within the minimal coding block, the luma intra prediction mode ofthe prediction block of the first luma signal, the chroma intraprediction mode of the prediction block of the chroma signal located ata reference position that is the same as the position of the predictionblock of the first luma signal, the luma intra prediction mode of theprediction block of the second luma signal, the luma intra predictionmode of the prediction block of the third luma signal, and the lumaintra prediction mode of the prediction block of the fourth luma signal,by coding information relating to the prediction mode of the minimalcoding block.

According to further another aspect of the present invention, there isalso provided a picture coding device that performs intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and codes information relating to an intra predictionmode, and the picture coding device includes: a luma signal intraprediction unit (103) that, when an intra prediction of the picturesignal is made in units of minimal coding blocks set in advance, in acase where a partition mode in which the luma signal is partitionedhorizontally and vertically is set, sets prediction blocks of first tofourth luma signals acquired by partitioning the luma signal of theminimal coding block horizontally and vertically and predicts a lumasignal based on neighboring blocks of coded luma signals in accordancewith a luma intra prediction mode for each prediction block of the lumasignal; a chroma signal intra prediction unit (103) that, in a casewhere the partition mode is set, and a chroma format is 4:4:4, setsprediction blocks of first to fourth chroma signals acquired bypartitioning the chroma signal of the minimal coding block horizontallyand vertically and predicts the chroma signal based on neighboringblocks of coded chroma signals in accordance with a chroma intraprediction mode for each prediction block of the chroma signal; and abitstream constructing unit (113) that constructs a bitstream in whichinformation relating to the prediction modes is arranged in order of,within the minimal coding block, the luma intra prediction mode of theprediction block of the first luma signal, the chroma intra predictionmode of the prediction block of the first chroma signal located at areference position that is the same as the position of the predictionblock of the first luma signal, the luma intra prediction mode of theprediction block of the second luma signal, the chroma intra predictionmode of the prediction block of the second chroma signal located at areference position that is the same as the position of the predictionblock of the second luma signal, the luma intra prediction mode of theprediction block of the third luma signal, the chroma intra predictionmode of the prediction block of the third chroma signal located at areference position that is the same as the position of the predictionblock of the third luma signal, the luma intra prediction mode of theprediction block of the fourth luma signal, and the chroma intraprediction mode of the prediction block of the fourth chroma signallocated at a reference position that is the same as the position of theprediction block of the fourth luma signal by coding informationrelating to the prediction mode of the minimal coding block.

According to further another aspect of the present invention, there isalso provided a picture coding device that performs intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and codes information relating to an intra predictionmode, and the picture coding device includes: a luma signal intraprediction unit (103) that, when an intra prediction of the picturesignal is made in units of minimal coding blocks set in advance, in acase where a partition mode in which the luma signal is partitionedhorizontally and vertically is set, sets prediction blocks of first tofourth luma signals acquired by partitioning the luma signal of theminimal coding block horizontally and vertically and predicts a lumasignal based on neighboring blocks of coded luma signals in accordancewith a luma intra prediction mode for each prediction block of the lumasignal; a chroma signal intra prediction unit (103) that, in a casewhere the partition mode is set, and a chroma format is 4:2:2, setsprediction blocks of first and second chroma signals acquired byhorizontally partitioning the chroma signal of the minimal coding blockand predicts the chroma signal based on neighboring blocks of codedchroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signal; and a bitstream constructingunit (113) that constructs a bitstream in which information relating tothe prediction modes is arranged in order of, within the minimal codingblock, the luma intra prediction mode of the prediction block of thefirst luma signal, the chroma intra prediction mode of the predictionblock of the first chroma signal located at a reference position that isthe same as the position of the prediction block of the first lumasignal, the luma intra prediction mode of the prediction block of thesecond luma signal, the luma intra prediction mode of the predictionblock of the third luma signal, the chroma intra prediction mode of theprediction block of the second chroma signal located at a referenceposition that is the same as the position of the prediction block of thethird luma signal, and the luma intra prediction mode of the predictionblock of the fourth luma signal by coding information relating to theprediction mode of the minimal coding block.

According to further another aspect of the present invention, there isprovided a picture coding method for performing intra prediction codingof a picture signal including a luma signal and a chroma signal in unitsof blocks and coding information relating to an intra prediction mode,and the picture coding method includes: when an intra prediction of thepicture signal is made in units of minimal coding blocks set in advance,in a case where a partition mode in which the luma signal is partitionedhorizontally and vertically is set, making an intra prediction of thechroma signal in units of prediction blocks of the intra prediction ofthe chroma signal within the minimal coding block set in accordance witha chroma format; and constructing a bitstream in which informationrelating to a luma intra prediction mode of the prediction block of theluma signal and information relating to a chroma intra prediction modeof the prediction block of the chroma signal located at a referenceposition that is the same as the position of the prediction block of theluma signal are continuous.

According to further another aspect of the present invention, there isalso provided a picture coding method for performing intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and coding information relating to an intraprediction mode, and the picture coding method includes: when an intraprediction of the picture signal is made in units of minimal codingblocks set in advance, in a case where a partition mode in which theluma signal is partitioned horizontally and vertically is set, settingprediction blocks of first to fourth luma signals acquired bypartitioning the luma signal of the minimal coding block horizontallyand vertically and predicting a luma signal based on neighboring blocksof coded luma signals in accordance with a luma intra prediction modefor each prediction block of the luma signal; in a case where thepartition mode is set, and a chroma format is 4:2:0, setting aprediction block of the chroma signal without partitioning the chromasignal of the minimal coding block and predicting a chroma signal basedon neighboring blocks of coded chroma signals in accordance with achroma intra prediction mode; and constructing a bitstream in whichinformation relating to the prediction modes is arranged in order of,within the minimal coding block, the luma intra prediction mode of theprediction block of the first luma signal, the chroma intra predictionmode of the prediction block of the chroma signal located at a referenceposition that is the same as the position of the prediction block of thefirst luma signal, the luma intra prediction mode of the predictionblock of the second luma signal, the luma intra prediction mode of theprediction block of the third luma signal, and the luma intra predictionmode of the prediction block of the fourth luma signal by codinginformation relating to the prediction mode of the minimal coding block.

According to further another aspect of the present invention, there isalso provided a picture coding method for performing intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and coding information relating to an intraprediction mode, and the picture coding method includes: when an intraprediction of the picture signal is made in units of minimal codingblocks set in advance, in a case where a partition mode in which theluma signal is partitioned horizontally and vertically is set, settingprediction blocks of first to fourth luma signals acquired bypartitioning the luma signal of the minimal coding block horizontallyand vertically and predicting a luma signal based on neighboring blocksof coded luma signals in accordance with a luma intra prediction modefor each prediction block of the luma signal; in a case where thepartition mode is set, and a chroma format is 4:4:4, setting predictionblocks of first to fourth chroma signals acquired by partitioning thechroma signal of the minimal coding block horizontally and verticallyand predicting the chroma signal based on neighboring blocks of codedchroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signal; and constructing a bitstreamin which information relating to the prediction modes is arranged inorder of, within the minimal coding block, the luma intra predictionmode of the prediction block of the first luma signal, the chroma intraprediction mode of the prediction block of the first chroma signallocated at a reference position that is the same as the position of theprediction block of the first luma signal, the luma intra predictionmode of the prediction block of the second luma signal, the chroma intraprediction mode of the prediction block of the second chroma signallocated at a reference position that is the same as the position of theprediction block of the second luma signal, the luma intra predictionmode of the prediction block of the third luma signal, the chroma intraprediction mode of the prediction block of the third chroma signallocated at a reference position that is the same as the position of theprediction block of the third luma signal, the luma intra predictionmode of the prediction block of the fourth luma signal, and the chromaintra prediction mode of the prediction block of the fourth chromasignal located at a reference position that is the same as the positionof the prediction block of the fourth luma signal by coding informationrelating to the prediction mode of the minimal coding block.

According to further another aspect of the present invention, there isalso provided a picture coding method for performing intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and coding information relating to an intraprediction mode, and the picture coding method includes: when an intraprediction of the picture signal is made in units of minimal codingblocks set in advance, in a case where a partition mode in which theluma signal is partitioned horizontally and vertically is set, settingprediction blocks of first to fourth luma signals acquired bypartitioning the luma signal of the minimal coding block horizontallyand vertically and predicting a luma signal based on neighboring blocksof coded luma signals in accordance with a luma intra prediction modefor each prediction block of the luma signal; in a case where thepartition mode is set, and a chroma format is 4:2:2, setting predictionblocks of first and second chroma signals acquired by horizontallypartitioning the chroma signal of the minimal coding block andpredicting the chroma signal based on neighboring blocks of coded chromasignals in accordance with a chroma intra prediction mode for eachprediction block of the chroma signal; and constructing a bitstream inwhich information relating to the prediction modes is arranged in orderof, within the minimal coding block, the luma intra prediction mode ofthe prediction block of the first luma signal, the chroma intraprediction mode of the prediction block of the first chroma signallocated at a reference position that is the same as the position of theprediction block of the first luma signal, the luma intra predictionmode of the prediction block of the second luma signal, the luma intraprediction mode of the prediction block of the third luma signal, thechroma intra prediction mode of the prediction block of the secondchroma signal located at a reference position that is the same as theposition of the prediction block of the third luma signal, and the lumaintra prediction mode of the prediction block of the fourth luma signalby coding information relating to the prediction mode of the minimalcoding block.

According to an aspect of the present invention, there is provided apicture decoding device that performs intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, andthe picture decoding device includes: an intra prediction unit (206)that, when an intra prediction of the picture signal is made in units ofcoding blocks, in a case where a chroma format is 4:2:2, in a mode forsetting a chroma intra prediction mode in accordance with a luma intraprediction mode, sets a chroma intra prediction mode based on the lumaintra prediction mode and the chroma format and makes an intraprediction of the chroma signal.

According to another aspect of the present invention, there is alsoprovided a picture decoding device that performs intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks by decoding information relating to an intraprediction mode, and the picture decoding device includes: a bitstreamdecoding unit (203) that consecutively decodes information relating to aluma intra prediction mode of a prediction block of a luma signal andinformation relating to a chroma intra prediction mode of a predictionblock of a chroma signal based on a bitstream in which the informationrelating to the luma intra prediction mode of the prediction block ofthe luma signal and the information relating to the chroma intraprediction mode of the prediction block of the chroma signal located ata reference position that is the same as the position of the predictionblock of the luma signal are continuous; and an intra prediction unit(206) that, when an intra prediction of the picture signal is made inunits of minimal decoding blocks set in advance, in a case where apartition mode in which the luma signal is partitioned horizontally andvertically is set, makes an intra prediction of the chroma signal basedon the decoded chroma intra prediction mode in units of predictionblocks of the intra prediction of the chroma signal within the minimaldecoding block set in accordance with a chroma format.

According to further another aspect of the present invention, there isalso provided a picture decoding device that performs intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks by decoding information relating to an intraprediction mode, and the picture decoding device includes: a bitstreamdecoding unit (203) that derives a partition mode in which the lumasignal is partitioned horizontally and vertically when an intraprediction of a picture signal is made in units of minimal decodingblocks set in advance and decodes information relating to a luma intraprediction mode for each prediction block of the luma signal andinformation relating to a chroma intra prediction mode for eachprediction block of the chroma signal based on a bitstream in whichcoding information relating to the prediction mode is arranged; a lumasignal intra prediction unit (206) that, in a case where the partitionmode is set, sets prediction blocks of first to fourth luma signalsacquired by partitioning the luma signal of the minimal decoding blockhorizontally and vertically and predicts the luma signal based on theneighboring blocks of decoded luma signals in accordance with each lumaintra prediction mode acquired based on the information relating to theluma intra prediction mode for each prediction block of the decoded lumasignal; and a chroma signal intra prediction unit (206) that, in a casewhere the partition mode is set, and a chroma format is 4:4:4, setsprediction blocks of first to fourth chroma signals acquired bypartitioning the chroma signal of the minimal decoding blockhorizontally and vertically and predicts the chroma signal based onneighboring blocks of decoded chroma signals in accordance with eachchroma intra prediction mode that is acquired based on the informationrelating to the chroma intra prediction mode for each prediction blockof the decoded chroma signal. The chroma signal intra prediction unit(206), in a case where the chroma format is 4:4:4 and a mode for settingthe chroma intra prediction mode in accordance with the luma intraprediction mode is designated based on the information relating to thechroma intra prediction mode for each prediction block of the decodedchroma signal, sets chroma intra prediction modes of first, second,third, and fourth chroma signals by using values representing the lumaintra prediction modes of the prediction blocks of the first, second,third, and fourth luma signals within the minimal decoding block asvalues representing the chroma intra prediction modes of the predictionblocks of the first, second, third, and fourth chroma signals within theminimal decoding block that are located at respective same referencepositions.

According to further another aspect of the present invention, there isalso provided a picture decoding device that performs intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks by decoding information relating to an intraprediction mode, and the picture decoding device includes: a bitstreamdecoding unit (203) that derives a partition mode in which the lumasignal is partitioned horizontally and vertically when an intraprediction of a picture signal is made in units of minimal decodingblocks set in advance and decodes information relating to a luma intraprediction mode for each prediction block of the luma signal andinformation relating to a chroma intra prediction mode for eachprediction block of the chroma signal based on a bitstream in whichcoding information relating to the prediction mode is arranged; a lumasignal intra prediction unit (206) that, in a case where the partitionmode is set, sets prediction blocks of first to fourth luma signalsacquired by partitioning the luma signal of the minimal decoding blockhorizontally and vertically and predicts the luma signal based onneighboring blocks of decoded luma signals in accordance with each lumaintra prediction mode acquired based on the information relating to theluma intra prediction mode for each prediction block of the decoded lumasignal; and a chroma signal intra prediction unit (206) that, in a casewhere the partition mode is set, and a chroma format is 4:2:2, setsprediction blocks of first and second chroma signals acquired bypartitioning the chroma signal of the minimal decoding blockhorizontally and vertically and predicts the chroma signal based onneighboring blocks of decoded chroma signals in accordance with eachchroma intra prediction mode that is acquired based on the informationrelating to the chroma intra prediction mode for each prediction blockof the decoded chroma signal. The chroma signal intra prediction unit(206), in a case where the chroma format is 4:2:2 and a mode for settingthe chroma intra prediction mode in accordance with the luma intraprediction mode is designated based on the information relating to thechroma intra prediction mode for each prediction block of the decodedchroma signal, sets chroma intra prediction modes of prediction blocksof the first and second chroma signals by converting values representingthe luma intra prediction modes of the prediction blocks of the firstand third luma signals within the minimal decoding block into valuesrepresenting the chroma intra prediction modes of the prediction blocksof the first and second chroma signals within the minimal decoding blockthat are located at respective same reference positions in accordancewith a conversion rule set in advance.

According to further another aspect of the present invention, there isprovided a picture decoding method for performing intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks by decoding information relating to an intraprediction mode, and the picture decoding method includes, when an intraprediction of the picture signal is made in units of coding blocks, in acase where a chroma format is 4:2:2, in a mode for setting a chromaintra prediction mode in accordance with a luma intra prediction mode,setting a chroma intra prediction mode based on the luma intraprediction mode and the chroma format and making an intra prediction ofthe chroma signal.

According to further another aspect of the present invention, there isalso provided a picture decoding method for performing intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks by decoding information relating to an intraprediction mode, and the picture decoding method includes: consecutivelydecoding information relating to a luma intra prediction mode of aprediction block of a luma signal and information relating to a chromaintra prediction mode of a prediction block of a chroma signal based ona bitstream in which the information relating to the luma intraprediction mode of the prediction block of the luma signal and theinformation relating to the chroma intra prediction mode of theprediction block of the chroma signal located at a reference positionthat is the same as the position of the prediction block of the lumasignal are continuous; and when an intra prediction of the picturesignal is made in units of minimal decoding blocks set in advance, in acase where a partition mode in which the luma signal is partitionedhorizontally and vertically is set, making an intra prediction of thechroma signal based on the decoded chroma intra prediction mode in unitsof prediction blocks of the intra prediction of the chroma signal withinthe minimal decoding block set in accordance with a chroma format.

According to further another aspect of the present invention, there isalso provided a picture decoding method for performing intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks by decoding information relating to an intraprediction mode, and the picture decoding method includes: deriving apartition mode in which the luma signal is partitioned horizontally andvertically when an intra prediction of a picture signal is made in unitsof minimal decoding blocks set in advance and decoding informationrelating to a luma intra prediction mode for each prediction block ofthe luma signal and information relating to a chroma intra predictionmode for each prediction block of the chroma signal based on a bitstreamin which coding information relating to the prediction mode is arranged;in a case where the partition mode is set, setting prediction blocks offirst to fourth luma signals acquired by partitioning the luma signal ofthe minimal decoding block horizontally and vertically and predictingthe luma signal based on the neighboring blocks of decoded luma signalsin accordance with each luma intra prediction mode acquired based on theinformation relating to the luma intra prediction mode for eachprediction block of the decoded luma signal; and in a case where thepartition mode is set, and a chroma format is 4:4:4, setting predictionblocks of first to fourth chroma signals acquired by partitioning thechroma signal of the minimal decoding block horizontally and verticallyand predicting the chroma signal based on neighboring blocks of decodedchroma signals in accordance with each chroma intra prediction mode thatis acquired based on the information relating to the chroma intraprediction mode for each prediction block of the decoded chroma signal.In the setting of prediction blocks and predicting the chroma signal, ina case where the chroma format is 4:4:4 and a mode for setting thechroma intra prediction mode in accordance with the luma intraprediction mode is designated based on the information relating to thechroma intra prediction mode for each prediction block of the decodedchroma signal, chroma intra prediction modes of prediction blocks offirst, second, third, and fourth chroma signals are set by using valuesrepresenting the luma intra prediction modes of the prediction blocks ofthe first, second, third, and fourth luma signals within the minimaldecoding block as values representing the chroma intra prediction modesof the prediction blocks of the first, second, third, and fourth chromasignals within the minimal decoding block that are located at respectivesame reference positions.

According to further another aspect of the present invention, there isalso provided a picture decoding method for performing intra predictiondecoding of a picture signal including a luma signal and a chroma signalin units of blocks by decoding information relating to an intraprediction mode, and the picture decoding method includes: deriving apartition mode in which the luma signal is partitioned horizontally andvertically when an intra prediction of a picture signal is made in unitsof minimal decoding blocks set in advance and decoding informationrelating to a luma intra prediction mode for each prediction block ofthe luma signal and information relating to a chroma intra predictionmode for each prediction block of the chroma signal based on a bitstreamin which coding information relating to the prediction mode is arranged;in a case where the partition mode is set, setting prediction blocks offirst to fourth luma signals acquired by partitioning the luma signal ofthe minimal decoding block horizontally and vertically and predictingthe luma signal based on neighboring blocks of decoded luma signals inaccordance with each luma intra prediction mode acquired based on theinformation relating to the luma intra prediction mode for eachprediction block of the decoded luma signal; and in a case where thepartition mode is set, and a chroma format is 4:2:2, setting predictionblocks of first and second chroma signals acquired by partitioning thechroma signal of the minimal decoding block horizontally and verticallyand predicting the chroma signal based on neighboring blocks of decodedchroma signals in accordance with each chroma intra prediction mode thatis acquired based on the information relating to the chroma intraprediction mode for each prediction block of the decoded chroma signal.In the setting of prediction blocks and predicting of the chroma signal,in a case where the chroma format is 4:2:2 and a mode for setting thechroma intra prediction mode in accordance with the luma intraprediction mode is designated based on the information relating to thechroma intra prediction mode for each prediction block of the decodedchroma signal, chroma intra prediction modes of prediction blocks of thefirst and second chroma signals are set by converting valuesrepresenting the luma intra prediction modes of the prediction blocks ofthe first and third luma signals within the minimal decoding block intovalues representing the chroma intra prediction modes of the predictionblocks of the first and second chroma signals within the minimaldecoding block that are located at respective same reference positionsin accordance with a conversion rule set in advance.

In addition, an arbitrary combination of constituent elements describedabove and any conversion of the representation of the present inventionamong a device, a system, a recording medium, a computer program, andthe like are also effective as aspects of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that illustrates the configuration of apicture coding device according to an embodiment;

FIG. 2 is a block diagram that illustrates the configuration of apicture decoding device according to an embodiment;

FIGS. 3A to 3E are diagrams that illustrate chroma formats of a picture;

FIGS. 4A to 4C are diagrams that illustrate units in which switchingbetween intra prediction modes according to an AVC/H.264 mode isperformed;

FIGS. 5A to 5H are diagrams that illustrate units in which an interprediction according to the AVC/H.264 mode is made;

FIG. 6 is a diagram that illustrates tree blocks and coding blocksdefined in this example;

FIGS. 7A to 7D are diagrams that illustrate partition modes defined inthis example;

FIG. 8 is a diagram that illustrates values of intra prediction modesand prediction directions defined in this example;

FIG. 9 is a diagram that illustrates an example of the positions ofblocks defined in this example;

FIG. 10 is a diagram that illustrates an example of the definition ofsyntax at the time of coding chroma format information using thesequence parameter set that is a header for coding information relatingto coding the entire sequence defined in this example;

FIGS. 11A to 11D are diagrams that illustrate methods of partitioningchroma signals of a coding block for N×N partition at the time ofperforming an intra prediction defined in this example;

FIG. 12 is a block diagram that illustrates the configuration of asecond bitstream constructing unit of the picture coding deviceaccording to the embodiment;

FIG. 13 is a block diagram that illustrates the configuration of asecond bitstream decoding unit of the picture decoding device accordingto the embodiment;

FIG. 14 is a conversion table used for calculating the value of a chromaintra prediction mode based on the value of a syntax element used on thedecoding side and the value of a luma intra prediction mode of aprediction block that is located at the same position as the position ofa prediction block of a chroma signal that is defined in this example;

FIG. 15 is a conversion table used for calculating the value of a chromaintra prediction mode based on the value of a luma intra prediction modeof a prediction block located at the same position as the position of aprediction block of chroma signals in a case where the chroma format is4:2:2 that is defined in this example;

FIG. 16 is a conversion table used for calculating the value of a syntaxelement relating to the chroma intra prediction mode based on the valueof the chroma intra prediction mode used on the coding side defined inthis embodiment and the value of the luma intra prediction mode of aprediction block located at the same position as the position of theprediction block of the chroma signal, in other words, the predictionblock of a luma signal belonging to the same prediction unit;

FIGS. 17A to 17C are diagrams that illustrate the sequences of entropycoding or decoding of a syntax element relating to the luma intraprediction mode and the chroma intra prediction mode according to anembodiment;

FIG. 18 illustrates an example of a syntax rule for coding and decodingcoding information in units of coding blocks that is defined in thisexample;

FIG. 19 illustrates an example of a syntax rule used for coding anddecoding coding information of a prediction unit that is defined in thisexample;

FIG. 20 is a flowchart that illustrates the processing sequence of acoding process in units of coding blocks and prediction blocks that isperformed by the second bitstream constructing unit according to theembodiment;

FIG. 21 is a flowchart that illustrates the sequence of a common codingprocess that is used in steps S1003, S1007, S1010, and S1013, which areillustrated in FIG. 20, according to the embodiment;

FIG. 22 is a flowchart that illustrates the sequence of a common codingprocess that is used in steps S1005, S1009, S1012, and S1015, which areillustrated in FIG. 20, according to the embodiment;

FIG. 23 is a flowchart that illustrates the processing sequence of adecoding process in units of coding blocks and prediction blocks that isperformed by the second bitstream decoding unit according to theembodiment;

FIG. 24 is a flowchart that illustrates the sequence of a commondecoding process that is used in steps S2003, S2007, S2010, and S2013,which are illustrated in FIG. 23, according to the embodiment;

FIG. 25 is a flowchart that illustrates the sequence of a commondecoding process that is used in steps S2005, S2009, S2012, and S2015,which are illustrated in FIG. 23, according to the embodiment;

FIG. 26 is a flowchart that illustrates the sequence of the process ofcalculating the value of a chroma intra prediction mode used in stepS2202, which is illustrated in FIG. 25, according to the embodiment;

FIGS. 27A and 27B are diagrams that illustrate the correspondencerelation between the prediction directions of intra predictions of aluma signal and a chroma signal in a case where the chroma format is4:2:2; and

FIGS. 28A and 28B are diagrams that illustrate the correspondencerelation between the prediction directions of intra predictions of aluma signal and a chroma signal in a case where the chroma format is4:2:0.

DETAILED DESCRIPTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

This embodiment relates to coding a moving picture, and, moreparticularly, in units of blocks acquired by partitioning a picture intorectangles having an arbitrary size and an arbitrary shape, reducing thecoding amount by using an intra prediction for making a prediction basedon the pixel value of a neighboring block that is in a state in whichcoding and decoding have been completed in a coding process and decodinghas been completed in a decoding process (hereinafter, the state isassumed in which decoding has been completed) and an inter predictionmade through motion compensation based on a picture that has beendecoded.

First, technologies and technical terms used in this example will bedefined.

Chroma Format

In description of the embodiment, the chroma formats of a picture thatis a target for coding and decoding are assumed to be monochrome, 4:2:0,4:2:2, and 4:4:4 that are set as targets also in the AVC/H.264 mode, andcoding and decoding are performed with a luma signal and a chroma signalbeing set as a set. However, the description of the chroma signal willnot be presented for the case of the monochrome. In addition, in amethod for independently coding luma signals and chroma signals in thechroma format of 4:4:4, in this example, the chroma format is assumed tobe the monochrome.

Tree Block and Coding Block

According to the embodiment, as illustrated in FIG. 6, the inside of ascreen is uniformly partitioned in units of squares having a samearbitrary size. This unit is defined as a tree block and is set as abasic unit for address management that is performed for specifying acoding/decoding target block (a coding target block in the codingprocess and a decoding target block in the decoding process) within thepicture. The tree block is configured by one luma signal and two chromasignals except for the case of the monochrome. The size of the treeblock can be freely set to be a size of the power of “2” in accordancewith the picture size or the texture within the screen. The tree blockcan optimize the coding process in accordance with the texture withinthe screen and, as is necessary, can form blocks having a small size byhierarchically partitioning luma signals and chroma signals within thetree block into four parts (forming each two partitions vertically andhorizontally). These blocks are defined as coding blocks and are used asbasic units at the time of performing coding and decoding. The codingblock is configured by one luma signal and two chroma signals except forthe case of the monochrome. A maximum size of the coding block is thesame as the size of the tree block. A coding block of a minimum size ofthe coding block will be referred to as a minimal coding block and canbe freely set to have a size of the power of “2”.

As illustrated in FIG. 6, a coding block A is formed as one coding blockwithout partitioning the tree block. A coding block B is a coding blockacquired by partitioning the tree block into four parts. A coding blockC is a coding block that is acquired by partitioning the tree block intofour parts and partitioning one of the four parts into four parts. Acoding block D is a coding block that is acquired by partitioning thetree block into four parts and hierarchically partitioning one of thefour parts into four parts twice and is a coding block of a minimalsize.

In description made here, it is assumed that the chroma format is 4:2:0,the size of the tree block is set to be 64×64 pixels in a luma signaland 32×32 pixels in a chroma signal, and the size of the minimal codingblock is set to be 8×8 pixels in the luma signal and 4×4 pixels in thechroma signal. In the case illustrated in FIG. 6, the size of the codingblock A is 64×64 pixels in the luma signal and 32×32 pixels in thechroma signal, the size of the coding block B is 32×32 pixels in theluma signal and 16×16 pixels in the chroma signal, the size of thecoding block C is 16×16 pixels in the luma signal and 8×8 pixels in thechroma signal, and the size of the coding block D is 8×8 pixels in theluma signal and 4×4 pixels in the chroma signal. In addition, in a casewhere the chroma format is 4:4:4, the sizes of the luma signal and thechroma signal of each coding block are the same. In a case where thechroma format is 4:2:2, the size of the coding block A is 32×64 pixelsin the chroma signal, the size of the coding block B is 16×32 pixels inthe chroma signal, the size of the coding block C is 8×16 pixels in thechroma signal, and the size of the coding block D, which is the minimalcoding block, is 4×8 pixels in the chroma signal.

Prediction Mode

In units of coding blocks, switching between an intra prediction formaking a prediction based on neighboring coded/decoded picture signalsand an inter prediction for making a prediction based on picture signalsof a coded/decoded picture is performed. A mode for identifying theintra prediction or the inter prediction is defined as a prediction modePredMode. The prediction mode PredMode has a value of the intraprediction MODE_INTRA or the inter prediction (MODE_INTER) and is usedfor selective coding.

Partition Mode, Prediction Block, and Prediction Unit

In a case where the intra prediction and the inter prediction are madewith the inside of a screen being partitioned into blocks, in order tofurther decrease the units in which switching between the intraprediction and the inter prediction is performed, the prediction is madewith the coding block being partitioned as is necessary. A mode used foridentifying the method of partitioning luma signals and chroma signalsof the coding block is defined as a partition mode PartMode. Inaddition, the partitioned block is defined as a prediction block. Asillustrated in FIGS. 7A to 7D, four types of partition modes PartModeare defined in accordance with the methods of partitioning luma signalsof the coding block. A partition mode PartMode in which a coding blockis regarded as one prediction block without partitioning luma signals ofthe coding block (FIG. 7A) is defined as 2N×2N partition PART_2N×2N, apartition mode PartMode in which a coding block is regarded as twoprediction blocks by partitioning luma signals of the coding block intotwo parts in the horizontal direction (FIG. 7B) is defined as 2N×Npartition PART_2N×N, a partition mode PartMode in which a coding blockis regarded as two prediction blocks by partitioning luma signals of thecoding block into two parts in the vertical direction (FIG. 7C) isdefined as N×2N partition PART_N×2N, and a partition mode PartMode inwhich a coding block is regarded as four prediction blocks bypartitioning luma signals of the coding block into four parts throughhorizontal and vertical equal partitioning (FIG. 7D) is defined as N×Npartition PART_N×N. In addition, chroma signals are also partitionedwith the same vertical and horizontal partition ratios of luma signalsfor each partition mode PartMode except for the case of the N×Npartition PART_N×N of the intra prediction MODE_INTRA. The vertical andhorizontal partition ratios of chroma signals of the coding block of theN×N partition PART_N×N of the intra prediction MODE_INTRA differ inaccordance with the type of the chroma format, which will be describedlater.

Inside the coding block, in order to specify each prediction block,numbers starting from “0” are assigned to prediction blocks presentinside the coding block in order of coding. These numbers are defined aspartition indexes PartIdx. A number written inside each prediction blockof a coding block illustrated in FIGS. 7A to 7D represents the partitionindex PartIdx of the prediction block. In the 2N×N partition PART_2N×Nillustrated in FIG. 7B, the partition index PartIdx of the upperprediction block is set as “0”, and the partition index PartIdx of thelower prediction block is set as “1”. In the N×2N partition PART_N×2Nillustrated in FIG. 7C, the partition index PartIdx of the leftprediction block is set as “0”, and the partition index PartIdx of theright prediction block is set as “1”. In the N×N partition PART_N×Nillustrated in FIG. 7D, the partition index PartIdx of the upper leftprediction block is set as “0”, the partition index PartIdx of the upperright prediction block is set as “1”, the partition index PartIdx of thelower left prediction block is set as “2”, and the partition indexPartIdx of the lower right prediction block is set as “3”.

In addition, since prediction blocks of a luma signal and a chromasignal that are located at the same position have a high correlation inboth the intra prediction and the inter prediction, in the embodiment, acoding process and a decoding process are performed for codinginformation of prediction blocks of a luma signal and a chroma signal asone prediction unit. In addition, a partition index PartIdx is alsoassigned to the prediction unit, and a partition index PartIdx of a samevalue is assigned to the prediction blocks of a luma signal and a chromasignal that are located at the same position.

In a case where the prediction mode PredMode is the intra predictionMODE_INTRA, for a coding block other than the coding block D (in thisexample, 8×8 pixels in the luma signal) that is the minimal codingblock, the 2N×2N partition PART_2N×2N is defined as the partition modePartMode. On the other hand, only for the coding block D that is theminimal coding block, the 2N×2N partition PART_2N×2N and the N×Npartition PART_N×N are defined as the partition modes PartMode.

In a case where the prediction mode PredMode is the inter predictionMODE_INTER, for a coding block other than the coding block D that is theminimal coding block, the 2N×2N partition PART_2N×2N, the 2N×N partitionPART_2N×N, and the N×2N partition PART_N×2N are defined as the partitionmodes PartMode. On the other hand, only for the coding block D that isthe minimal coding block, the N×N partition PART_N×N is defined as thepartition mode PartMode in addition to the 2N×2N partition PART_2N×2N,the 2N×N partition PART_2N×N, and the N×2N partition PART_N×2N. Thereason for not defining the N×N partition PART_N×N in a coding blockother than the minimal coding block is that, for a coding block otherthan the minimal coding block, a small coding block can be representedby partitioning the coding block into four parts.

Intra Prediction and Intra Prediction Mode

In an intra prediction, the values of pixels of the processing targetblock are predicted based on values of pixels of a neighboring decodedblock within the same screen. In a coding device and a decoding deviceof this example, one of intra prediction modes of 34 kinds is selected,and the intra prediction is made. FIG. 8 is a diagram that illustratesvalues of the intra prediction modes and prediction directions definedin this example. The direction indicated by a solid-line arrowrepresents a prediction direction of the intra prediction, in otherwords, a direction that is referred to in the intra prediction, and theintra prediction of a pixel located at a start point of the arrow ismade by referring to a decoded pixel in the direction indicated by thearrow in a neighboring block. Each number represents a value of theintra prediction mode. As the intra prediction modes intraPredMode, inaddition to a vertical prediction (intra prediction modeintraPredMode=0) that makes a prediction in the vertical direction fromthe decoded block located on the upper side, a horizontal prediction(intra prediction mode intraPredMode=1) that makes a prediction in thehorizontal direction from the decoded block located on the left side, anaverage prediction (intra prediction mode intraPredMode=2) that makes aprediction by calculating an average value from a neighboring decodedblock, and an average prediction (intra prediction mode intraPredMode=3)that makes a prediction at the angle of the inclination of 45 degreesfrom a neighboring decoded block, angle predictions (intra predictionmodes intraPredMode=4 to 33) that make predictions of 30 kinds formaking predictions in directions inclined at various angles from aneighboring decoded block are defined.

The intra prediction mode is prepared respectively for luma signals andchroma signals, the intra prediction mode for luma signals is defined asa luma intra prediction mode, and the intra prediction mode for chromasignals is defined as a chroma intra prediction mode. In the coding anddecoding of the luma intra prediction mode, a structure is used in whichthe correlation with the luma intra prediction mode of a neighboringblock is used, in a case where it is determined that a prediction can bemade based on the luma intra prediction mode of a neighboring block onthe coding side, information used for specifying the block that isreferred to is transmitted, and, in a case where it is determined thatanother value may be preferably set to the luma intra prediction moderather than making a prediction based on the luma intra prediction modeof a neighboring block, the value of the luma intra prediction mode isfurther coded or decoded. By predicting the luma intra prediction modeof the coding/decoding target block based on the luma intra predictionmode of the neighboring block, the amount of codes to be transmitted canbe reduced. On the other hand, in the coding and decoding of the chromaintra prediction mode, a structure is used in which the correlation withthe luma intra prediction mode of a prediction block of luma signalsthat is located at the same position as the position of a predictionblock of chroma signals is used, in a case where it is determined that aprediction can be made based on the luma intra prediction mode on thecoding side, a value of the chroma intra prediction mode is predictedbased on the value of the luma intra prediction mode, and, in a casewhere it is determined that an independent value may be preferably setto the chroma intra prediction mode rather than making a predictionbased on the luma intra prediction mode, the value of the chroma intraprediction mode is coded or decoded. By predicting the chroma intraprediction mode based on the luma intra prediction mode, the amount ofcodes to be transmitted can be reduced.

Transform Block

Similarly to a conventional case, also in this embodiment, by using anorthogonal transform for transforming a discrete signal into a frequencydomain such as a discrete cosine transform (DCT) or a discrete sinetransform (DST) and an inverse transform thereof, the amount of codes isreduced. The transform or the inverse transform is performed in units oftransform blocks acquired by hierarchically partitioning a coding blockinto four parts. In the embodiment, four kinds of conversion sizes of32×32 pixels, 16×16 pixels, 8×8 pixels, and 4×4 pixels are defined, anda 32×32 transform, a 16×16 transform, an 8×8 transform, and a 4×4transform and inverse transforms thereof are performed.

Positions of Tree Block, Coding Block, Prediction Block, and TransformBlock

As the position of each block such as the tree block, the coding block,the prediction block, or the transform block described in this example,the position of a pixel of a luma signal that is located at an uppermostand leftmost position on the screen of luma signals is set as the origin(0, 0), and the position of a pixel of a luma signal that is located atthe uppermost and leftmost position included in the area of each blockis represented as two-dimensional coordinates (x, y). The directions ofthe coordinate axes, the rightward side in the horizontal direction andthe downward side in the vertical direction are set as positivedirections, and the unit is one pixel unit of a luma signal. Not only ina case where the chroma format is 4:4:4 in which the picture sizes (thenumbers of pixels) are the same in the luma signal and the chroma signalbut also in a case where the chroma format is 4:2:0 or 4:2:2 in whichthe picture sizes (the numbers of pixels) in the luma signal and thechroma signal are different from each other, the position of each blockof chroma signals is represented by using the coordinates of a pixel ofluma signals included in the area of the block, and the unit is onepixel of a luma signal. In this way, it is apparent that the position ofeach block of chroma signals can be specified, and, by only comparingthe values of coordinates, the relation between the positions of theblock of luma signals and the block of chroma signals becomes clear.FIG. 9 is a diagram that illustrates an example of the positions ofblocks defined in this example in a case where the chroma format is4:2:0. In FIG. 9, “x” represents the position of a pixel of a lumasignal on the plane of a screen, and “◯” represents the position of apixel of a chroma signal. A dotted-line rectangle illustrated in FIG. 9is a block E of luma signals of 8×8 pixels and is also a block F ofchroma signals of 4×4 pixels. In addition, “▴” is the position of apixel of a luma signal, which is located at an uppermost and leftmostposition, in the block E of the luma signals of the 8×8 pixelsrepresented by dotted lines. Accordingly, “▴” is the position of theblock E of the luma signals of the 8×8 pixels represented by dottedlines, and the coordinates of a luma signal of a pixel represented by“▴” are the coordinates of the block E of luma signals of the 8×8 pixelsrepresented by the dotted lines. Similarly, “▴” is the position of apixel of a luma signal, which is located at an uppermost and leftmostposition, included in the area of the block F of chroma signals of the4×4 pixels represented by the dotted lines as well. Accordingly, “▴” isthe position of the block F of chroma signals of 4×4 pixels representedby the dotted lines, and the coordinates of a luma signal of a pixelrepresented by “▴” are the coordinates of the block F of chroma signalsof the 4×4 pixels represented by the dotted lines. In the embodiment,regardless of the type of the chroma format and the shape and the sizeof the block, only in a case where the x component and the y componentof the coordinates of the block of luma signals, which is defined, andthe coordinates of the block of chroma signals are all the same, suchblocks are defined to be located at the same position.

FIG. 1 is a block diagram that illustrates the configuration of a movingpicture coding device according to the embodiment. The moving picturecoding device according to the embodiment is equipped with a chromaformat setting unit 101, a picture memory 102, an intra prediction unit103, an inter prediction unit 104, a coding method decision unit 105, aresidual signal generation unit 106, an orthogonaltransform/quantization unit 107, an inverse quantization/inverseorthogonal transform unit 108, a decoding picture signal superimpositionunit 109, a decoded picture memory 111, a first bitstream constructingunit 112, a second bitstream constructing unit 113, a third bitstreamconstructing unit 114, and a bitstream multiplexing unit 115.

The chroma format setting unit 101 sets the chroma format of a picturesignal that is a coding target. It may be configured such that a chromaformat is determined based on a coding picture signal supplied to thechroma format setting unit 101, and the chroma format is set, or achroma format may be externally set. The information of the chromaformat in which only the luma signal is set to 4:2:0, 4:2:2, or 4:4:4 issupplied to the first bitstream constructing unit 112 and also to thesecond bitstream constructing unit 113, and a coding process that isbased on the chroma format is performed. In addition, although notillustrated in the figure, also in the picture memory 102, the intraprediction unit 103, the inter prediction unit 104, the coding methoddecision unit 105, the residual signal generation unit 106, theorthogonal transform/quantization unit 107, the inversequantization/inverse orthogonal transform unit 108, the decoding picturesignal superimposition unit 109, and the third bitstream constructingunit 114 illustrated in FIG. 1, a coding process is performed based onthe set chroma format, and information is managed in the codinginformation storing memory 110 and the decoded picture memory 111 basedon the set chroma format.

In the picture memory 102, picture signals that are coding targetssupplied in order of time are temporarily stored. The picture signalsthat are coding targets stored in the picture memory 102 are sorted, arepartitioned in units of coding blocks in a plurality of combinationsaccording to the setting, are further partitioned in units of predictionblocks, and are supplied to the intra prediction unit 103 and the interprediction unit 104.

The intra prediction unit 103, in units of prediction blocks accordingto each partition mode PartMode in units of a plurality of codingblocks, makes intra predictions corresponding to a plurality of lumaintra prediction modes and chroma intra prediction modes for lumasignals and chroma signals of the prediction block that is a codingtarget based on the decoded picture signals stored in the decodedpicture memory 111, thereby acquiring intra prediction signals. Inaddition, as the chroma intra prediction mode, a value predicted basedon the luma intra prediction mode in accordance with the chroma formator one of “0” (horizontal direction), “1” (vertical direction), “2”(average), and “3” (inclination of 45 degrees), which are representativeintra prediction modes, is selected to be limited thereto. Here, amethod of predicting the chroma intra prediction mode based on the lumaintra prediction mode will be described later.

By subtracting an intra prediction signal in units of prediction blocksfrom the signal that is the coding target supplied in units ofprediction blocks for each pixel, a predicted residual signal isacquired. An evaluation value used for evaluating the code amount andthe distortion amount is calculated by using the predicted residualsignal, a mode that is optimal from the viewpoint of the code amount andthe distortion amount is selected in units of prediction blocks fromamong a plurality of intra prediction modes, and intra predictioninformation, an intra prediction signal, and an evaluation value of theintra prediction corresponding to the intra prediction mode selected asa candidate for the intra prediction of the prediction block aresupplied to the coding method decision unit 105. The predictionprocessing units in which the intra prediction is made will be describedlater.

The inter prediction unit 104 performs inter predictions according to aplurality of inter prediction modes (an L0 prediction, an L1 prediction,and both predictions) and a reference picture based on decoded picturesignals stored in the decoded picture memory 111 in units correspondingto the partition modes PartMode of a plurality of coding block units, inother words, in units of prediction blocks, thereby acquiring interprediction signals. At that time, a motion vector search is performed,and the inter prediction is made in accordance with the searched motionvector. In addition, in the case of the both predictions, by averagingtwo inter prediction signals for each pixel or performing weightedaddition thereof, the inter predictions of both the predictions areperformed. An inter prediction signal in units of prediction blocks issubtracted from the signal of the coding target supplied in units ofprediction blocks for each pixel, thereby deriving a predicted residualsignal. An evaluation value used for evaluating the code amount and thedistortion amount is calculated by using the predicted residual signal,a mode that is optimal from the viewpoint of the code amount and thedistortion amount is selected from among the plurality of interprediction modes in units of prediction blocks, and the inter predictioninformation, the inter prediction signal, and the evaluation value ofthe inter prediction corresponding to the selected inter prediction modeas a candidate for the inter prediction of the prediction block aresupplied to the coding method decision unit 105.

The coding method decision unit 105 determines a partition method, aprediction mode PredMode, and a partition mode PartMode of the codingblock, which is optimal, based on the intra prediction evaluation valuecorresponding to the intra prediction information and the interprediction evaluation value corresponding to the inter predictioninformation that are selected in each prediction block in units of aplurality of coding blocks, supplies coding information that includesthe intra prediction information or the inter prediction informationaccording to the determination to the second bitstream constructing unit113, stores the coding information in the coding information storingmemory 110, and supplies a prediction signal that has beenintra-predicted or inter-predicted according to the determination to theresidual signal generation unit 106 and the decoding picture signalsuperimposition unit 109.

The residual signal generation unit 106 generates a residual signal bysubtracting the prediction signal that has been intra-predicted orinter-predicted from the picture signal to be coded for each pixel andsupplies the residual signal to the orthogonal transform/quantizationunit 107.

The orthogonal transform/quantization unit 107 generates an orthogonallytransformed and quantized residual signal by performing an orthogonaltransform and quantization for transforming the residual signal to besupplied into a frequency domain such as a DCT or a DST in accordancewith a quantization parameter and supplies the orthogonally transformedand quantized residual signal to the third bitstream constructing unit114 and the inverse quantization/inverse orthogonal transform unit 108.

The first bitstream constructing unit 112 calculates values of syntaxelements relating to coding information in units of sequences, pictures,and slices in accordance with a semantics rule used for defining themeaning and the deriving method of the syntax elements, constructs afirst bitstream by performing entropy coding of the calculated value ofeach syntax element through variable-length coding, arithmetic coding,or the like in accordance with the syntax rule, and supplies the codedfirst bitstream to the bitstream multiplexing unit 115. In addition, thevalue of the syntax element relating to the chroma format is calculatedby the first bitstream constructing unit 112. The syntax elementrelating to the chroma formation is calculated based on the chromaformat information that is supplied from the chroma format setting unit101. FIG. 10 is an example of the definition of syntax at the time ofcoding the chroma format information using the sequence parameter setthat is a header used for coding information relating to coding of theentire sequence defined in this example. A syntax elementchroma_format_idc represents the type of the chroma format. As themeaning of the syntax chroma_format_idc, a value 0 representsmonochrome, a value 1 represents 4:2:0, a value 2 represents 4:2:2, anda value 3 represents 4:4:4. In addition, the meaning of the syntaxelement separate_colour_plane_flag represents whether or not a lumasignal and chroma signals are separately coded. A case where the valueof the syntax element separate_colour_plane_flag is “0” represents thattwo chroma signals are coded with being associated with the luma signal.A case where the value of the syntax element chroma_format_idc is “1”represents that the luma signal and the two chroma signals areseparately coded. Only in a case where the value of the syntax elementchroma_format_idc is “3”, in other words, in a case where the chromaformat is 4:4:4, the value of the syntax element chroma_format_idc canbe set to “0” or “1”, and, for any other chroma format, the value of thesyntax element separate_colour_plane_flag is constantly coded with being“0”.

The second bitstream constructing unit 113 calculates the value of thesyntax element relating to the coding information determined by thecoding method decision unit 105 for each prediction block in addition tothe coding information in units of coding blocks in accordance with thesemantics rule that defines the meaning and the deriving method of thesyntax element. More particularly, in addition to the coding informationin units of coding blocks such as the partition method, the predictionmode PredMode, and the partition mode PartMode of the coding block, thevalue of the syntax element relating to the coding information in unitsof prediction blocks is calculated. In a case where the prediction modePredMode is the intra prediction, the values of the syntax elementsrelating to the intra prediction mode including the luma intraprediction mode and the chroma intra prediction mode are calculated. Onthe other hand, in a case where the prediction mode PredMode is theinter prediction, the values of syntax elements relating to the interprediction mode, information used for specifying a reference picture,and the inter prediction information such as a motion vector arecalculated. Entropy coding using variable-length coding, arithmeticcoding, or the like is performed for the calculated value of each syntaxelement in accordance with the syntax rule, a second bitstream isconstructed, and the coded second bitstream is supplied to the bitstreammultiplexing unit 115. Detailed processing contents relating to thecalculation of syntax elements and the entropy coding relating to theluma intra prediction mode and the chroma intra prediction mode that areperformed by the second bitstream constructing unit 113 will bedescribed later.

The third bitstream constructing unit 114 constructs a third bitstreamby performing entropy coding of the orthogonally-transformed andquantized residual signal through the variable-length coding, arithmeticcoding, or the like in accordance with the defined syntax rule andsupplies the third bitstream to the bitstream multiplexing unit 115.

The bitstream multiplexing unit 115 constructs a bitstream bymultiplexing the first bitstream, the second bitstream, and the thirdbitstream in accordance with a defined syntax rule and outputs themultiplexed bitstream.

The inverse quantization/inverse orthogonal transform unit 108calculates a residual signal by performing inverse quantization andinverse orthogonal transform of the orthogonally-transformed andquantized residual signal that is supplied from the orthogonaltransform/quantization unit 107 and supplies the calculated residualsignal to the decoding picture signal superimposition unit 109. Thedecoding picture signal superimposition unit 109 constructs a decodedpicture by superimposing the prediction signal that has beenintra-predicted or inter-predicted in accordance with the determinationmade by the coding method decision unit 105 and the residual signal thathas been inversely-quantized and inversely-orthogonal transformed by theinverse quantization/inverse orthogonal transform unit 108 each otherand stores the constructed decoded picture in the decoded picture memory111. In addition, a filtering process for decreasing block distortion orthe like due to coding may be performed for the decoded picture, and theprocessed decoded picture may be stored in the decoded picture memory111.

FIG. 2 represents blocks that illustrate the configuration of a movingpicture decoding device, which corresponds to the moving picture codingdevice illustrated in FIG. 1, according to an embodiment. The movingpicture decoding device according to the embodiment is equipped with abitstream splitting unit 201, a first bitstream decoding unit 202, asecond bitstream decoding unit 203, a third bitstream decoding unit 204,a chroma format managing unit 205, an intra prediction unit 206, aninter prediction unit 207, an inverse quantization/inverse orthogonaltransform unit 208, a decoding picture signal superimposition unit 209,a coding information storing memory 210, a decoded picture memory 211,and switches 212 and 213.

A bitstream supplied to the bitstream splitting unit 201 is split inaccordance with a defined syntax rule, a first bitstream representingcoding information in units of sequences, pictures, and slices issupplied to the first bitstream decoding unit 202, a second bitstreamincluding coding information in units of coding blocks is supplied tothe second bitstream decoding unit 203, and a third bitstream includingan orthogonally transformed and quantized residual signal is supplied tothe third bitstream decoding unit 204.

The first bitstream decoding unit 202 performs entropy decoding of thesupplied first bitstream in accordance with a syntax rule and acquiresvalues of syntax elements relating to the coding information in units ofsequences, pictures, and slices. The coding information in units ofsequences, pictures, and slices is calculated based on values of syntaxelements relating to the coding information, which has been decoded, inunits of sequences, pictures, and slices in accordance with a semanticsrule used for defining the meaning and the deriving method of the syntaxelements. The first bitstream decoding unit 202 is a bitstream decodingunit that corresponds to the first bitstream constructing unit 112disposed on the coding side and has a function for returning thebitstream including the coding information in units of sequences,pictures, and slices, which has been coded by the first bitstreamconstructing unit 112 to each coding information. The chroma formatinformation coded by the first bitstream constructing unit 112 iscalculated based on the value of the syntax element relating to chromaformat information that is acquired by performing entropy decoding ofthe second bitstream using the first bitstream decoding unit 202. Inaccordance with the syntax rule illustrated in FIG. 10 and the semanticsrule, the type of the chroma format is specified based on the value ofthe syntax element chroma_format_idc, and, as the value of the syntaxelement chroma_format_idc, “0” represents monochrome, “1” represents4:2:0, “2” represents 4:2:2, and “3” represents 4:4:4. In addition, in acase where the value of the syntax element chroma_format_idc is “3”, thesyntax element separate_colour_plane_flag is decoded, and it isdetermined whether or not a luma signal and chroma signals areseparately coded. The calculated chroma format information is suppliedto the chroma format managing unit 205.

The chroma format managing unit 205 manages the supplied chroma formatinformation. The supplied chroma format information is supplied to thesecond bitstream decoding unit 203, and the process of calculatingcoding information of a coding block and a prediction block based on thechroma format information is performed. Although not illustrated in thefigure, also in the third bitstream decoding unit 204 and the intraprediction unit 206, the inter prediction unit 207, the inversequantization/inverse orthogonal transform unit 208, and the decodingpicture signal superimposition unit 209 illustrated in FIG. 2, adecoding process based on the chroma format information is performed,and data is managed based on the chroma format information in the codinginformation storing memory 210 and the decoded picture memory 211.

The second bitstream decoding unit 203 performs entropy decoding of thesupplied first bitstream in accordance with the syntax rule, therebyacquiring values of syntax elements relating to the coding informationin units of coding blocks and prediction blocks. In accordance with thesemantics rule that defines the meaning and deriving method of thesyntax elements, the coding information in units of coding blocks and inunits of prediction blocks is calculated based on the values of thesyntax elements relating to the supplied coding information in units ofcoding blocks and in units of prediction blocks. The second bitstreamdecoding unit 203 is a coding information calculating unit thatcorresponds to the second bitstream constructing unit 113 disposed onthe coding side and has a function for returning the second bitstreamincluding the coding information in units of coding blocks and in unitsof prediction blocks, which has been coded by the second bitstreamconstructing unit 113, to each coding information. More specifically,based on each syntax element acquired by decoding the second bitstreamin accordance with the defined syntax rule, in addition to the partitionmethod, the prediction mode PredMode, and the partition mode PartMode ofthe coding block, in a case where the prediction mode PredMode is theintra prediction, an intra prediction mode that includes the luma intraprediction mode and the chroma intra prediction mode is acquired. On theother hand, in a case where the prediction mode PredMode is the interprediction, inter prediction information such as the inter predictionmode, information used for specifying a reference picture, and a motionvector is acquired. In a case where the prediction mode PredMode is anintra prediction, the intra prediction mode including the luma intraprediction mode and the chroma intra prediction mode is supplied to theintra prediction unit 206 through the switch 212. In a case where theprediction mode PredMode is the inter prediction, the inter predictioninformation such as the inter prediction mode, information used forspecifying a reference picture, and a motion vector is supplied to theinter prediction unit 207 through the switch 212. Detailed processesrelating to the entropy decoding process performed by the secondbitstream decoding unit 203 and the process of calculating the values ofthe luma intra prediction mode and the chroma intra prediction modebased on the syntax elements relating to the luma intra prediction modeand the chroma intra prediction mode will be described later.

The third bitstream decoding unit 204 calculates an orthogonallytransformed and quantized residual signal by decoding the suppliedbitstream and supplies the orthogonally transformed and quantizedresidual signal to the inverse quantization/inverse orthogonal transformunit 208.

The intra prediction unit 206 generates a predicted picture signal byperforming an intra prediction based on a decoded neighboring blockstored in the decoded picture memory 211 in accordance with the suppliedintra prediction mode including the luma intra prediction mode and thechroma intra prediction mode and supplies the predicted picture signalto the decoding picture signal superimposition unit 209 through theswitch 213. In addition, the units in which the intra prediction is madewill be described later.

The inter prediction unit 207 generates a predicted picture signal bymaking an inter prediction using motion compensation based on thedecoded reference picture stored in the decoded picture memory 211 byusing the inter prediction mode, the information used for specifying thereference picture, and the inter prediction information such as a motionvector, which are to be supplied, and supplies the predicted picturesignal to the decoding picture signal superimposition unit 209 throughthe switch 213. In addition, in the case of the both predictions, afinal predicted picture signal is generated by adaptably multiplying twomotion compensation predicted picture signals of the L0 and L1predictions by weighing factors and superimposing the predicted picturesignals each other.

The inverse quantization/inverse orthogonal transform unit 208 performsan inverse orthogonal transform and inverse quantization of theorthogonally transformed and quantized residual signal that has beendecoded by the third bitstream decoding unit 204, thereby acquiring aninversely-orthogonal transformed and inversely-quantized residualsignal.

The decoding picture signal superimposition unit 209 decodes thedecoding picture signal by superimposing the predicted picture signalthat has been predicted by the intra prediction unit 206 or the interprediction unit 207 and the residual signal that has beeninversely-orthogonal transformed and inversely quantized by the inversequantization/inverse orthogonal transform unit 208 each other and storesthe decoding picture signal in the decoded picture memory 211. When thedecoded picture is stored in the decoded picture memory 211, a filteringprocess for decreasing block distortion or the like due to coding may beperformed for the decoded picture before the decoded picture is storedin the decoded picture memory 211. The decoding picture signals storedin the decoded picture memory 211 are output in the output order.

Next, the prediction processing units in which the intra prediction ismade, which is one of the features of the embodiment, will be describedin detail.

First, a minimal unit of the orthogonal transform according to thisexample will be described. By using a characteristic of picture codingin which, while degradation in the picture quality of a low frequencycomponent easily stands out, degradation in the picture quality of ahigh frequency component does not easily stand out, the code amount isreduced by quantizing the high frequency component more roughly than thelow frequency component. However, in the case of the 2×2 conversion, itis difficult to sufficiently divide the signal into sufficient number offrequency components, and accordingly, the reduction effectiveness ofthe code amount is low. In addition, in a case where the processing unitof the intra prediction, the transformation, and the quantization is toosmall, the number of processing units corresponding thereof increases,whereby the processing becomes complex. Thus, in this example, theminimal unit of the orthogonal transform is set as 4×4 pixels.

Next, a minimal unit of the intra prediction made in this example, inother words, a minimal size of the prediction block in the case of theintra prediction will be described. In the intra prediction, since thepixel value of the processing target block is predicted based on thepixel values of a neighboring block that has been decoded within thesame screen, it is necessary to complete the decoding process before thecoding and decoding process of the subsequent block. More specifically,by using the prediction signal acquired by the intra prediction, aresidual signal is calculated, an orthogonal transform, quantization,inverse-quantization, and inverse transform are performed for theresidual signal, and a resultant signal is superimposed with theprediction signal, whereby the decoding process is completed, and astate is formed in which an intra prediction of a subsequent block canbe made. Accordingly, it is necessary to perform the intra prediction inunits of which the size is equal to or larger than the size of theminimal transform block. The reason for this is that, when the intraprediction is made in units of which the size is smaller than the sizeof the minimal transform block, thereafter, an orthogonal transformcannot be performed, and the decoding process cannot be performed.Accordingly, in this example, a minimal unit of the intra prediction, inother words, a minimal size of the prediction block at the time ofperforming the intra prediction is set as 4×4 pixels that is the same asthe minimal unit of the orthogonal transform.

Next, a minimal size of the coding block according to this example willbe described. In the minimal coding block, the partition mode PartModeis defined to be the N×N partition in both the intra predictionMODE_INTRA and the inter prediction of the prediction mode PredMode.While the N×N partition is a partition mode PartMode in which a codingblock is partitioned into four prediction blocks through horizontal andvertical equal partition of luma signals of the coding block, theminimal unit of the intra prediction according to this example is set as4×4 pixels, and accordingly, the minimal size of the coding block is 8×8pixels in the luma signal.

Next, the method of partitioning chroma signals of the coding block forthe N×N partition at the time of performing an intra prediction will bedescribed. FIGS. 11A to 11D are diagrams that illustrate methods ofpartitioning chroma signals of a coding block for the N×N partition atthe time of performing the intra prediction.

In a case where the chroma format is 4:2:0, when the minimal size of thecoding block is 8×8 pixels in the luma signal, the minimal size of thecoding block is 4×4 pixels in the chroma signal, and the coding blockcannot be further partitioned. Thus, in this embodiment, in a case wherethe chroma format is 4:2:0, when the prediction mode is the intraprediction, and the partition mode PartMode is the N×N partition, asillustrated in FIG. 11A, an intra prediction is made in units of 4×4pixels with the coding block being partitioned into four predictionblocks through horizontal and vertical equal partition of the codingblock in the luma signal. However, in the chroma signal, as illustratedin FIG. 11B, the coding block is not partitioned and is set as oneprediction block, and an intra prediction is made in units of 4×4 pixelsof which the size is the same as the size of the prediction block ofluma signals. In addition, the partition index PartIdx of the predictionblock of chroma signals is set to “0”.

In addition, in a case where the chroma format is 4:2:2, when theminimal size of the coding block is 8×8 pixels in the luma signal, theminimal size of the coding block is 4×8 pixels in the chroma signal.Accordingly, while the coding block can be equally partitionedhorizontally, the coding block cannot be equally partitioned vertically.Therefore, in this embodiment, in the case where the chroma format is4:2:2, when the prediction mode is an intra prediction, and thepartition mode (PartMode) is N×N partition, as illustrated in FIG. 11A,in a luma signal, an intra prediction is made in units of 4×4 pixels forthe coding block as four prediction blocks acquired through horizontaland vertical equal partition. On the other hand, in a chroma signal, asillustrated in FIG. 11C, an intra prediction is made similarly in unitsof 4×4 pixels for the coding block as two prediction blocks acquiredthrough only the horizontal equal partition of the coding block withoutvertical partition thereof. In addition, the partition indexes PartIdxof the prediction blocks of chroma signals are set to “0” and “2” in thecoding order (order from the upper side to the lower side). The reasonfor setting the partition index PartIdx of the lower block to “2” isthat the lower prediction block of chroma signals is located at the sameposition as the position of the prediction block of which the partitionindex PartIdx of the luma signals is “2”.

The prediction block of chroma signals and the prediction block of lumasignals being at the same position represents that, when the coordinatesof the uppermost and leftmost pixel of each prediction block is set asthe reference position, the reference positions of the prediction blockof chroma signals and the prediction block of luma signals being thesame.

In a case where the chroma format is 4:4:4, when the minimal size of thecoding block is 8×8 pixels in the luma signal, the minimal size of thecoding block is 8×8 pixels in the chroma signal, and, similarly to theluma signal, the coding block can be partitioned into four predictionblocks through horizontal and vertical equal partition. Thus, in thisembodiment, in a case where the chroma format is 4:4:4, when theprediction mode is the intra prediction, and the partition mode PartModeis the N×N partition, as illustrated in FIG. 11A, in the luma signal, anintra prediction is made in units of 4×4 pixels with the coding blockbeing partitioned into four prediction blocks through horizontal andvertical equal partition of the coding block, and, also in the chromasignal, as illustrated in FIG. 11C, an intra prediction is made in unitsof 4×4 pixels with the coding block being partitioned into fourprediction blocks through horizontal and vertical equal partition of thecoding block. In addition, similarly to the luma signal, the partitionindexes PartIdx of the prediction blocks of chroma signals are set to“0”, “1”, “2”, and “3” in the coding order (the order of the upper leftside, the upper right side, the lower left side, and the lower rightside).

In the embodiment, regardless of the type of the chroma format, in acase where the values of the partition index PartIdx of the predictionblock of the luma signals and the partition index PartIdx of theprediction block of the chroma signals are the same, the coordinates(the coordinates of a pixel located at the uppermost and leftmostposition in the prediction block) representing the position of theprediction block of the luma signals and the coordinates (thecoordinates of a pixel located at the uppermost and leftmost position inthe prediction block) representing the position of the prediction blockof the chroma signals are the same, and accordingly, the predictionblocks are located at the same position.

Next, in a case where the chroma format is 4:2:0, a case will beconsidered in which a coding block is partitioned into four parts inboth the luma signal and the chroma signal through N×N partition of theinter prediction, and, a prediction block is formed such that the lumasignal is 4×4 pixels, and the chroma signal is 2×2 pixels. In the interprediction, in both the luma signal and the chroma signal, the interprediction is made through motion compensation using common codinginformation. However, in the motion compensation of a chroma signal ofwhich the chroma format is 4:2:0, a value acquired by scaling both thehorizontal and vertical components half in the magnitude of the value ofthe reference motion vector through the luma signal is used. In theinter prediction, as is different from the intra prediction, thedecoding signal of a neighboring block within the same picture is notused, and accordingly, an inter prediction processing unit that issmaller than the orthogonal transform processing unit can be used.Accordingly, since the orthogonal transform can be performed in unitslarger than the prediction block, even in a case where the coding blockis partitioned into four parts in the chroma signal, and the interprediction is made in units of 2×2 pixels, the orthogonal transform doesnot need to be performed necessarily in units of 2×2 pixels, and, bycombining four prediction blocks after the inter predictions of the fourprediction blocks and calculating a residual signal in units of 4×4pixels, the orthogonal transform can be performed in units of 4×4pixels.

Therefore, in the N×N partition of the inter prediction, regardless ofthe type of the chroma format, both the luma signals and the chromasignals are equally partitioned horizontally and vertically so as toform four prediction blocks.

Next, the coding process of the coding information in units of codingblocks and prediction blocks that is performed by the second bitstreamconstructing unit 113 illustrated in FIG. 1 will be described withfocusing on points relating to the intra prediction mode that is afeature of the embodiment. FIG. 12 is a block diagram that illustratesthe configuration of the second bitstream constructing unit 113illustrated in FIG. 1.

As illustrated in FIG. 12, the second bitstream constructing unit 113illustrated in FIG. 1 is configured by: a syntax element calculatingunit 121 relating to the coding information in units of coding blocks; asyntax element calculating unit 122 relating to the luma intraprediction mode; a syntax element calculating unit 123 relating to thechroma intra prediction mode; a syntax element calculating unit 124relating to the inter prediction information; an intra prediction modecoding control unit 125; and an entropy coding unit 126. In each unitconfiguring the second bitstream constructing unit 113, a processcorresponding to the chroma format information supplied from the chromaformat setting unit 101 is performed, and a process corresponding to thecoding information of the prediction mode, the partition mode PartMode,and the like in units of coding blocks is performed.

The syntax element calculating unit 121 relating to the codinginformation in units of coding blocks calculates the value of the syntaxelement relating to the coding information in units of coding blocks andsupplies the calculated value of the syntax element to the entropycoding unit 126. The values of the syntax elements relating to theprediction mode PredMode used for determining the intra predictionMODE_INTRA or the inter prediction MODE_INTER of the coding block andthe partition mode PartMode used for determining the shape of theprediction block are calculated by the syntax element calculating unit121 relating to the coding information in units of the coding blocks

The syntax element calculating unit 122 relating to the luma intraprediction mode, in a case where the prediction mode PredMode of thecoding block is the intra prediction MODE_INTRA, calculates the valuesof syntax element relating to the luma intra prediction mode of theprediction block of the luma signal and supplies the calculated value ofthe syntax element to the entropy coding unit 126. The syntax elementsrelating to the luma intra prediction mode are a syntax elementprev_intra_luma_pred_flag[x0][y0] that is a flag representing whether ornot a prediction can be made based on the luma intra prediction mode ofthe neighboring block, a syntax element mpm_idx[x0][y0] that is an indexindicating a prediction block as a prediction source, and a syntaxelement rem_intra_luma_pred_mode[x0][y0] that represents the luma intraprediction mode in units of prediction blocks. Here, x0 and y0 arecoordinates that represent the position of the prediction block. In thecalculation of the value of the syntax element relating to the lumaintra prediction mode, the correlation with the luma intra predictionmode of a neighboring block stored in the coding information storingmemory 110 is used. In a case where the prediction can be made based onthe luma intra prediction mode of the neighboring block, a syntaxelement prev_intra_luma_pred_flag[x0][y0], which is a flag representingthe use of the value, is set to “1” (true), and a value used forspecifying a reference destination is set to the syntax elementmpm_idx[x0][y0] that is an index indicating a prediction block of theprediction source. On the other hand, in a case where a predictioncannot be made, the syntax element prev_intra_luma_pred_flag[x0][y0] isset to “0” (false), and a value used for specifying the luma intraprediction mode is set to the syntax elementrem_intra_luma_pred_mode[x0][y0] that represents the luma intraprediction mode to be coded.

The number of luma intra prediction modes of the prediction block withinthe coding block differs in accordance with the partitioned block. Thus,in a case where the partition mode PartMode is the 2N×2N partition, thevalues of the syntax elements relating to the luma intra prediction modeof the prediction blocks of one set are calculated for each codingblock. In a case where the partition mode is the N×N partition, thevalues of the syntax elements relating to the luma intra predictionmodes of prediction blocks of four sets are calculated for each codingblock.

The syntax element calculating unit 123 relating to the chroma intraprediction mode, in a case where the prediction mode PredMode of thecoding block is the intra prediction MODE_INTRA, calculates the value ofthe syntax element intra_chroma_pred_mode[x0][y0] relating to the chromaintra prediction mode of the prediction block of chroma signals andsupplies the calculated value of the syntax elementintra_chroma_pred_mode[x0][y0] to the entropy coding unit 126. In thecalculation of the value of the syntax element relating to the chromaintra prediction mode, the correlation with the luma intra predictionmode of the prediction block of luma signals that is located at the sameposition as the position of the prediction block of chroma signals isused. Thus, in a case where a chroma intra prediction mode can bepredicted based on the luma intra prediction mode of the predictionblock of luma signals that is located at the same position as theposition of the prediction block of chroma signals, the value of thechroma intra prediction mode is predicted based on the value of the lumaintra prediction mode. On the other hand, in a case where the chromaintra prediction mode cannot be predicted based on the luma intraprediction mode, a structure is used in which any one of values “0”(horizontal direction), “1” (horizontal direction), “2” (average value),and “3” (inclination of 45 degrees), which are representative in intraprediction modes, is set to the chroma intra prediction mode. As aresult, the code amount is reduced.

Here, a method of predicting the value of the chroma intra predictionmode based on the value of the luma intra prediction mode and the valueof the syntax element relating to the chroma intra prediction mode onthe decoding side will be described. FIG. 14 is a conversion table usedfor calculating the value of the chroma intra prediction mode based onthe value of the syntax element intra_chroma_pred_mode[x0][y0] relatingto the chroma intra prediction mode defined in this example and thevalue of the luma intra prediction mode of the prediction block locatedat the same position as the position of the prediction block of chromasignals. By using this conversion table, the value of the chroma intraprediction mode is calculated on the decoding side.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “0”, the value of the chroma intraprediction mode is predicted in accordance with the chroma format basedon the value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofchroma signals.

In a case where the chroma format is 4:2:0 or 4:4:4, and the value ofthe syntax element intra_chroma_pred_mode[x0][y0] is“0”, the value ofthe luma intra prediction mode of the prediction block located at thesame position as the position of the prediction block of chroma signalsis directly set as the value of the chroma intra prediction mode.

In a case where the chroma format is 4:2:2 and the value of the syntaxelement intra_chroma_pred_mode[x0][y0] is “0”, based on a conversiontable illustrated in FIG. 15, the value of the chroma intra predictionmode is calculated in accordance with the value of the luma intraprediction mode of the prediction block located at the same position asthe position of the prediction block of chroma signals. FIG. 15 is aconversion table used for predicting the value of the chroma intraprediction mode based on the value of the luma intra prediction mode ofthe prediction block located at the same position as the position of theprediction block of chroma signals in a case where the chroma format is4:2:2 that is defined in this example.

In a case where the chroma format is 4:2:2, when the value of the chromaintra prediction mode is predicted based on the value of the luma intraprediction mode, the reason for not using the original value, unlike thecase of the chroma format of 4:2:0 or 4:4:4, but calculating the valueusing the conversion table illustrated in FIG. 15 will be described. Thechroma format of 4:2:2, as illustrated in FIG. 3B, is a chroma format inwhich chroma signals are sampled to have a half density of the densityof luma signals in the horizontal direction and to have the same densityas the density of the luma signals in the vertical direction.Accordingly, when an intra prediction of a chroma signal is performed ina prediction direction acquired by performing ½ times scaling in thehorizontal direction for each prediction direction of the luma intraprediction mode or in a prediction direction neighboring thereto, aresult that is the same as or close to that of the intra prediction ofthe luma signal of the prediction block located at the same position asthe position of the prediction block of the chroma signal is acquired.

This will be described in detail with reference to FIGS. 27A and 27B.FIGS. 27A and 27B are diagrams that illustrate the correspondencerelation between the prediction directions of intra predictions of aluma signal and a chroma signal in a case where the chroma format is4:2:2. In FIGS. 27A and 27B, “x” represents the position of a pixel of aluma signal, and “◯” represents the position of a pixel of a chromasignal. In the case where the chroma format is 4:2:2, the chroma signalsare sampled in the horizontal direction at a half ratio of that of lumasignals. FIG. 27A represents the positions of sampled pixels of lumasignals and chroma signals of 4:2:2. Reference sign P1 represents apixel that is intra-predicted, and reference sign P2 represents a pixel(actually, a pixel neighboring thereto is also referred to due to afiltering process) that is referrer to at the time of making the intraprediction. An arrow, which is denoted by reference sign 2701, directingfrom the pixel P1 to the pixel P2 represents the intra predictiondirection of the pixel P1 of the luma signal.

FIG. 27B represents the array of pixels of chroma signals that have beensampled at a half ratio in the horizontal direction. Here, when an intraprediction of a chroma signal is made, in a case where ½ scaling is notperformed in the horizontal direction, the intra prediction direction ofthe pixel P1 of the chroma signal is the direction of an arrow denotedby reference sign 2702, and in the pixel array of chroma signals, thepixel denoted by reference sign P3 is incorrectly referred to. However,the correct reference destination is a pixel denoted by reference signP2. Thus, by performing ½-times scaling in the horizontal direction forthe intra prediction direction of the luma signal to be set as the intraprediction direction of the chroma signal, as denoted by reference sign2703, a correct intra prediction direction for the array of chromasignals is calculated, and a pixel neighboring to the upper side that isa correct reference destination located at the end in the intraprediction direction is derived.

In FIGS. 27A and 27B, although a case has been described in which apixel that is neighboring to the upper side of a prediction block isreferred to, a case may be similarly applied in which a pixel that isneighboring to the left side thereof is referred to. In the case of apixel neighboring to the left side, by performing two-times scaling inthe vertical direction for the intra prediction direction of the lumasignal (this is the same as deriving the direction of a vector byperforming ½-times scaling in the vertical direction), a correct intraprediction direction for the array of chroma signals is calculated, anda pixel (including a pixel that is partially neighboring to the upperside) neighboring to the left side that is a correct referencedestination located at the end in the intra prediction direction isderived.

Thus, in the conversion table illustrated in FIG. 15, as denoted bydotted-line arrows illustrated in FIG. 8, when the values of the lumaintra prediction mode in which reference destinations are aligned in thehorizontal direction (on the horizontal axis) are 3, 18, 10, 19, 4, 20,11, 21, 0, 22, 12, 23, 5, 24, 13, 25, and 6, by performing ½ timesscaling of such values in the horizontal direction, values of the chromaintra prediction modes in the prediction direction closest to thecalculated prediction direction are selected, and the values of thechroma intra prediction modes are respectively set to 19, 4, 20, 20, 11,11, 21, 0, 0, 0, 22, 12, 12, 23, 23, 5, and 24. Here, performing ½ timescaling of the prediction direction of the intra prediction in thehorizontal direction is the same as performing two-times scaling thereofin the vertical direction. Thus, when an intra prediction of a chromasignal is performed in a prediction direction derived by performingtwo-times scaling of each prediction direction of the luma intraprediction mode in the vertical direction or in a prediction directionneighboring thereto, a result of the prediction that is the same as orclose to that of the intra prediction of the luma signal of theprediction block located at the same position as the position of theprediction block of chroma signals is derived. Accordingly, in theconversion table illustrated in FIG. 15, as illustrated in FIG. 8, whenthe values of the luma intra prediction mode in which referencedestinations are aligned in the vertical direction (on the verticalaxis) are 26, 14, 27, 7, 28, 15, 29, 1, 30, 16, 31, 8, 32, 17, 33, and9, by performing two-times scaling of such values in the verticaldirection, values of the chroma intra prediction modes in a predictiondirection closest to the calculated prediction direction are selected,and the values of the chroma intra prediction modes are respectively setto 10, 18, 3, 26, 27, 28, 15, 1, 16, 31, 32, 33, 9, 9, 9, and 9.

On the other hand, in a case where the chroma format is 4:2:0 or 4:4:4,when the value of the chroma intra prediction mode is predicted based onthe value of the luma intra prediction mode, the intra predictiondirection of the luma signal and the intra prediction direction of thechroma signal coincide with each other, and the value of the luma intraprediction mode does not need to be converted into the value of thechroma intra prediction mode. This will be described with reference toFIGS. 28A and 28B. FIGS. 28A and 28B are diagrams that illustrate thecorrespondence relation between the prediction directions of intrapredictions of a luma signal and a chroma signal in a case where thechroma format is 4:2:0. FIG. 28A illustrates the arrangement of lumasignals and chroma signals in the case where the chroma format is 4:2:0.The chroma signals are sampled at a half ratio horizontally andvertically. An arrow, which is denoted by reference sign 2704 from apixel P1 to a pixel P2 represents the intra prediction direction of thepixel P1 of the luma signal. In this case, also in the arrangement ofchroma signals illustrated in FIG. 28B, the intra prediction directionof the luma signal is, as denoted by reference sign 2705, directly theintra prediction direction of the chroma signal, and accordingly, thepixel P2 that is the reference destination of the pixel P1 of the chromasignal can be correctly referred to.

In addition, in consideration of the above-described points, in a casewhere the value of the chroma intra prediction mode is predicted, theintra prediction unit 103 predicts the value of the chroma intraprediction mode based on the value of the luma intra prediction mode ofthe prediction block located at the same position as the position of theprediction block of the chroma signal in accordance with the chromaformat. In other words, in a case where the chroma format is 4:2:0 or4:4:4, and the value of the chroma intra prediction mode is predicted,the value of the luma intra prediction mode of a prediction blocklocated at the same position as the position of the prediction block ofthe chroma signal is directly set as the value of the chroma intraprediction mode. In a case where the chroma format is 4:2:2, and thevalue of the chroma intra prediction mode is predicted, based on theconversion table illustrated in FIG. 15, the value of the chroma intraprediction mode is calculated in accordance with the value of the lumaintra prediction mode of the prediction block located at the sameposition as the position of the prediction block of the chroma signal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is in the range of “1” to “4”, the valueof the chroma intra prediction mode is calculated based on a combinationof the value of the syntax element intra_chroma_pred_mode[x0][y0] andthe value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofthe chroma signal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “1”, the value of the chroma intraprediction mode takes the value of “0” or “1” in accordance with thevalue of the luma intra prediction mode of a prediction block located atthe same position as the position of the prediction block of the chromasignal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “2”, the value of the chroma intraprediction mode takes the value of “1” or “2” in accordance with thevalue of the luma intra prediction mode of a prediction block located atthe same position as the position of the prediction block of the chromasignal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “3”, the value of the chroma intraprediction mode takes the value of “2” or “3” in accordance with thevalue of the luma intra prediction mode of a prediction block located atthe same position as the position of the prediction block of the chromasignal.

In a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “4”, the value of the chroma intraprediction mode takes the value of “3”.

FIG. 16 is a conversion table used for calculating the value of a syntaxelement intra_chroma_pred_mode[x0][y0] relating to the chroma intraprediction mode based on the value of the chroma intra prediction modeand the value of the luma intra prediction mode of a prediction blocklocated at the same position as the position of the prediction block ofthe chroma signal, in other words, the prediction block of a luma signalbelonging to the same prediction unit. The conversion table illustratedin FIG. 16 corresponds to the conversion table illustrated in FIG. 14.By using the conversion table illustrated in FIG. 16, on the codingside, the value of the syntax element intra_chroma_pred_mode[x0][y0] iscalculated.

In a case where the value of the chroma intra prediction mode is “0”,the value of the syntax element intra_chroma_pred_mode[x0][y0] takes thevalue of “0” or “1” in accordance with the value of the luma intraprediction mode of a prediction block located at the same position asthe position of the prediction block of the chroma signal.

In a case where the value of the chroma intra prediction mode is “1”,the value of the syntax element intra_chroma_pred_mode[x0][y0] takes thevalue of “0”, “1”, or “2” in accordance with the value of the luma intraprediction mode of a prediction block located at the same position asthe position of the prediction block of the chroma signal.

In a case where the value of the chroma intra prediction mode is “2”,the value of the syntax element intra_chroma_pred_mode[x0][y0] takes thevalue of “0”, “2”, or “3” in accordance with the value of the luma intraprediction mode of a prediction block located at the same position asthe position of the prediction block of the chroma signal.

In a case where the value of the chroma intra prediction mode is “3”,the value of the syntax element intra_chroma_pred_mode[x0][y0] takes thevalue of “0”, “3”, or “4” in accordance with the value of the luma intraprediction mode of a prediction block located at the same position asthe position of the prediction block of the chroma signal.

In a case where the value of the chroma intra prediction mode is in therange of “4” to “33”, it is represented that the chroma intra predictionmode is predicted based on the value of the luma intra prediction modeof a prediction block located at the same position, and the value of thesyntax element intra_chroma_pred_mode[x0][y0] takes the value of “0”.However, in a case where the chroma format is 4:2:2, and the value ofthe chroma intra prediction mode is predicted, the intra prediction unit103, based on the conversion table illustrated in FIG. 15, calculatesthe value of the chroma intra prediction mode in accordance with thevalue of the luma intra prediction mode of a prediction block located atthe same position as the position of the prediction block of the chromasignal, and accordingly, the value of the chroma intra prediction modecan take any one of 4, 5, 9, 10, 11, 12, 15, 16, 18, 19, 20, 21, 22, 23,24, 26, 27, 28, 31, 32, and 33.

In order to specify a prediction block of the luma signal that islocated at the same position as the position of the prediction block ofthe chroma signal, the partition index PartIdx that specifies eachprediction block may be referred to, or the coordinates that representthe position of each prediction block may be referred to.

In addition, since the number of chroma intra prediction modes ofprediction blocks within a coding block is different in accordance withthe type of the chroma format supplied from the chroma format settingunit 101, in a case where the chroma format is 4:2:0, the value of thesyntax element relating to the chroma intra prediction mode of oneprediction block is calculated for each coding block.

Furthermore, the number of chroma intra prediction modes of predictionblocks within a coding block is different in accordance with acombination of the partition mode and the chroma format, and, in a casewhere the partition mode is 2N×2N partition, the value of the syntaxelement relating to the chroma intra prediction mode of one predictionblock is calculated for each coding block regardless of the type of thechroma format. In a case where the partition mode is N×N partition, andthe chroma format is 4:2:0, the value of the syntax element relating tothe luma intra prediction mode of one prediction block is calculated foreach coding block. In a case where the partition mode is N×N partition,and the chroma format is 4:2:2, the value of the syntax element relatingto the luma intra prediction mode of two prediction blocks is calculatedfor each coding block. In a case where the partition mode is N×Npartition, and the chroma format is 4:4:4, the value of the syntaxelement relating to the luma intra prediction mode of four predictionblocks is calculated for each coding block.

In a case where the prediction mode PredMode of the coding block is theinter prediction MODE_INTER, the syntax element calculating unit 124relating to the inter prediction information calculates the value of thesyntax element relating to the inter prediction information in units ofprediction blocks and supplies the calculated value of each syntaxelement to the entropy coding unit 126. In the inter predictioninformation in units of prediction blocks, information such as the interprediction mode (the L0 prediction, the L1 prediction, or bothpredictions), an index used for specifying a plurality of referencepictures, and a motion vector is included.

The entropy coding unit 126 performs entropy coding of the value of thesyntax element relating to the coding information in units of codingblocks that is supplied from the syntax element calculating unit 121relating to the coding information in units of coding blocks, the valueof the syntax element relating to the luma intra prediction mode of theprediction block of the luma signal that is supplied from the syntaxelement calculating unit 122 relating to the luma intra prediction mode,the value of the syntax element relating to the chroma intra predictionmode of the prediction block of the chroma signal that is supplied fromthe syntax element calculating unit 123 relating to the chroma intraprediction mode, and the value of the syntax element relating to theinter prediction information in units of prediction blocks that issupplied from the syntax element calculating unit 124 relating to theinter prediction information in accordance with a syntax rule set inadvance. At that time, the intra prediction mode coding control unit 125controls the sequence of the entropy coding of the luma intra predictionmode and the chroma intra prediction mode in accordance with thepartition mode and the chroma format, and the entropy coding unit 126performs the entropy coding process of the luma intra prediction modeand the chroma intra prediction mode in the sequence directed by theintra prediction mode coding control unit 125.

Hereinafter, the sequence of the entropy coding of the luma intraprediction mode and the chroma intra prediction mode at the time of theN×N partition, which is performed by the entropy coding unit 126controlled by the intra prediction mode coding control unit 125, will bedescribed. FIGS. 17A to 17C are diagrams that illustrate entropy codingor decoding sequences of syntax elements relating to the luma intraprediction mode and the chroma intra prediction mode according to theembodiment. FIGS. 17A, 17B, and 17C illustrate the entropy coding anddecoding sequences in a case where the chroma formats are respectively4:2:0, 4:2:2, and 4:4:4. Here, L0, L1, L2, and L3 represent that thepartition indexes PartIdx of luma signals are syntax elements relatingto the luma intra prediction modes of “0”, “1”, “2”, and “3”. Inaddition, C0, C1, C2, and C3 represent that the partition indexesPartIdx of chroma signals are syntax elements relating to the chromaintra prediction modes of the prediction blocks of “0”, “1”, “2”, and“3”

In a case where the chroma format is 4:2:0, right after L0 is coded, C0is coded, and, subsequently, L1, L2, and L3 are coded (C1, C2, and C3are neither present nor coded).

In a case where the chroma format is 4:2:2, L0 is coded, C0 is codedright after L0, subsequently, L1 and L2 are coded, C2 is coded rightafter L2, and subsequently, L3 is coded (C1 and C3 are neither presentnor coded).

In a case where the chroma format is 4:4:4, L0 is coded, C0 is codedright after L0, and subsequently, L1, C1, L2, C2, L3, and C3 aresequentially coded.

In other words, the luma intra prediction mode and the chroma intraprediction mode belonging to the same prediction unit are consecutivelycoded.

In a case where entropy coding is performed in the coding sequenceillustrated in FIGS. 17A to 17C, there are following advantages.

As a first advantage, when the value of the chroma intra prediction modeis calculated based on the value of the syntax element relating to thechroma intra prediction mode that is acquired by performing entropydecoding the bitstream on the decoding side, there is an advantage ofsimplifying the processing.

In the coding sequence illustrated in FIGS. 17A to 17C, the chroma intraprediction mode is constantly calculated regardless of the predictionmode, the partition mode, and the chroma format by referring to thevalue of the intra prediction mode calculated based on the syntaxelement relating to the luma intra prediction mode that has beenpreviously coded, whereby the processing can be simplified.

As a second advantage, when the prediction mode is the intra prediction,and the partition mode is N×N partition, there is an advantage ofshortening the delay time of a series of processes relating to the intraprediction of a prediction block of a chroma signal on the decodingside.

In the coding sequence illustrated in FIGS. 17A to 17C, right afterentropy coding is performed for the syntax element L0 relating to theluma intra prediction mode of the prediction block of a luma signal, byperforming entropy coding of the syntax element C0 relating to thechroma intra prediction mode of the prediction block of a chroma signalthat is located at the same position as the position of the predictionblock of a luma signal belonging to the same prediction unit, on thedecoding side, right after entropy decoding is performed for the syntaxelement L0 relating to the luma intra prediction mode of the predictionblock of a luma signal, entropy decoding can be performed for the syntaxelement C0 relating to the chroma intra prediction mode of theprediction block of a chroma signal that is located at the same positionas the position of the prediction block of the luma signal, and thecalculation of the chroma intra prediction mode can be quickly started.Accordingly, the intra prediction process of the chroma signal performedthereafter can be quickly started, and, in a case where an intraprediction of a prediction block of a luma signal and an intraprediction of a prediction block of a chroma signal are performed inparallel with each other, the delay time of each process relating to thechroma signal can be shortened. In addition, in a case where the chromaformat is 4:2:2 or 4:4:4, as the intra prediction process of theprediction block of a chroma signal having “0” as the partition indexPartIdx corresponding to C0 is quickly started, the intra predictionprocess of a prediction block having a partition index PartIdx as beinga value other than “0” referring to the decoding signal of theprediction block of the chroma signal having “0” as the partition indexPartIdx can be quickly started. In addition, by performing coding of thesyntax element C0 relating to the chroma intra prediction mode beforethe syntax element L1 relating to the luma intra prediction mode, on thedecoding side, the start of the entropy decoding process of the syntaxelements L1, L2, and L3 relating to the luma intra prediction mode isdelayed. However, in order to start the intra prediction process of theprediction block corresponding to L1, a series of decoding processes (anintra prediction, inverse quantization, and inverse orthogonalconversion) relating to a prediction block corresponding to L0 to bereferred to at the time of the intra prediction needs to be completed,and accordingly, there is scarcely a disadvantage due to the delay ofthe entropy decoding of L1, L2, and L3.

Next, the decoding process of coding information in units of codingblocks and prediction blocks that is performed by the second bitstreamdecoding unit 203 illustrated in FIG. 2 will be described with focusingon points relating to the intra prediction mode that is a feature of theembodiment. FIG. 13 is a block diagram that illustrates theconfiguration of the second bitstream decoding unit 203 illustrated inFIG. 2.

As illustrated in FIG. 13, the second bitstream decoding unit 203illustrated in FIG. 2 is configured by: an intra prediction modedecoding control unit 221; an entropy decoding unit 222; a codinginformation calculating unit 223 in units of coding blocks; a luma intraprediction mode calculating unit 224; a chroma intra prediction modecalculating unit 225; and an inter prediction information calculatingunit 226. Each unit configuring the second bitstream decoding unit 203performs the process according to the chroma format information suppliedfrom the chroma format managing unit 205 and performs the processaccording to the coding information such as the prediction mode and thepartition mode in units of coding blocks.

The entropy decoding unit 222 performs entropy decoding of a bitstreamincluding coding information in units of coding blocks and predictionblocks, which is supplied from the bitstream splitting unit, inaccordance with a syntax rule set in advance and derives the value ofthe syntax element relating to the coding information in units of codingblocks, the value of the syntax element relating to the luma intraprediction mode of the prediction block of luma signals, the value ofthe syntax element relating to the chroma intra prediction mode of theprediction block of chroma signals, and the value of the syntax elementrelating to the inter prediction information in units of predictionblocks. At that time, the intra prediction mode decoding control unit221 controls the sequence of the entropy decoding of the luma intraprediction mode and the chroma intra prediction mode in accordance withthe partition mode and the chroma format, and the entropy decoding unit222 performs the entropy decoding process of the luma intra predictionmode and the chroma intra prediction mode in the sequence directed bythe intra prediction mode decoding control unit 221. The intraprediction mode decoding control unit 221 is a control unit thatcorresponds to the intra prediction mode coding control unit 125disposed on the coding side and sets the decoding sequence of the intraprediction mode, which is the same as the coding sequence of the intraprediction mode set by the intra prediction mode coding control unit125, in accordance with the partition mode and the chroma format andcontrols the decoding sequence of the intra prediction mode of theentropy decoding unit 222. The entropy decoding unit 222 is a decodingunit that corresponds to the entropy coding unit 126 disposed on thecoding side and performs entropy decoding in accordance with the samerule as the syntax rule used by the entropy coding unit 126. In otherwords, the decoding process of the intra prediction mode is performed inthe same sequence as the coding sequence illustrated in FIGS. 17A to17C. In other words, an luma intra prediction mode and a chroma intraprediction mode belonging to the same prediction unit are consecutivelydecoded.

The value of the syntax element relating to the coding information inunits of coding blocks, which has been acquired by being decoded, issupplied to the coding information calculating unit 223 in units ofcoding blocks, the value of the syntax element relating to the lumaintra prediction mode of the prediction block of luma signals issupplied to the luma intra prediction mode calculating unit 224, thevalue of the syntax element relating to the chroma intra prediction modeof the prediction block of chroma signals is supplied to the chromaintra prediction mode calculating unit 225, and the value of the syntaxelement relating to the inter prediction information in units ofprediction blocks is supplied to the inter prediction informationcalculating unit 226.

The coding information calculating unit 223 in units of coding blockscalculates the coding information in units of coding blocks based on thesupplied value of the syntax element relating to the coding informationin units of the coding blocks and supplies the calculated codinginformation to the intra prediction unit 206 or the inter predictionunit 207 through the switch 212.

The coding information calculating unit 223 in units of coding blocks isa coding information calculating unit that corresponds to the syntaxelement calculating unit 121 relating to the coding information in unitsof coding blocks disposed on the coding side and performs calculation inaccordance with the same semantics rule. The values relating to theprediction mode PredMode used for determining either the intraprediction MODE_INTRA or the inter prediction MODE_INTER of the codingblock and the partition mode PartMode used for determining the shape ofthe prediction block are calculated by the coding informationcalculating unit 223 in units of coding blocks.

In a case where the prediction mode PredMode of the coding block that iscalculated by the coding information calculating unit 223 in units ofcoding blocks is the intra prediction MODE_INTRA, the luma intraprediction mode calculating unit 224 calculates the luma intraprediction mode of the prediction block of luma signals based on thesupplied value of the syntax element relating to the luma intraprediction mode of the prediction block of luma signals, supplies thecalculated luma intra prediction mode to the chroma intra predictionmode calculating unit 225, and supplies the calculated luma intraprediction mode to the intra prediction unit 206 through the switch 212.The luma intra prediction mode calculating unit 224 is a codinginformation calculating unit that corresponds to the syntax elementcalculating unit 122 relating to the luma intra prediction mode disposedon the coding side and performs calculation in accordance with the samesemantics rule. As the syntax elements relating to the luma intraprediction mode, there are a syntax elementprev_intra_luma_pred_flag[x0][y0] that is a flag representing whether ornot a prediction can be made based on the luma intra prediction mode ofa neighboring block, a syntax element mpm_idx[x0][y0] that is an indexindicating a prediction block of a prediction source, and a syntaxelement rem_intra_luma_pred_mode[x0][y0] that represents the luma intraprediction mode in units of prediction blocks. In the calculation of theluma intra prediction mode, the correlation with the luma intraprediction mode of a neighboring block stored in the coding informationstoring memory 210 is used. In a case where the prediction can be madebased on the luma intra prediction mode of the neighboring block, thesyntax element prev_intra_luma_pred_flag[x0][y0], which is a flagrepresenting the use of the value, is “1” (true), and the luma intraprediction mode of the neighboring prediction block that is directedbased on the syntax element mpm_idx[x0][y0] that is an index indicatingthe prediction block of a prediction source is set as the luma intraprediction mode of the prediction mode. On the other hand, in a casewhere the syntax element prev_intra_luma_pred_flag[x0][y0] is “0”(false), the luma intra prediction mode is not predicted based on theneighboring prediction block, but the luma intra prediction mode iscalculated based on the value of the syntax elementrem_intra_luma_pred_mode[x0][y0] that represents the decoded luma intraprediction mode.

The number of luma intra prediction modes of the prediction block withinthe coding block differs in accordance with the partition mode. Thus, ina case where the partition mode is the 2N×2N partition, the values ofthe luma intra prediction mode of one set of prediction blocks arecalculated for each coding block. On the other hand, in a case where thepartition mode is the N×N partition, the values of the luma intraprediction modes of four sets of prediction blocks are calculated foreach coding block.

The chroma intra prediction mode calculating unit 225, in a case wherethe prediction mode PredMode of the coding block, which is calculated bythe coding information calculating unit 223 in units of coding blocks,is the intra prediction MODE_INTRA, calculates the value of the chromaintra prediction mode based on the supplied value of the syntax elementintra_chroma_pred_mode[x0][y0] relating to the chroma intra predictionmode of the prediction block of chroma signals and the value of the lumaintra prediction mode that is supplied from the luma intra predictionmode calculating unit and supplies the calculated value of the chromaintra prediction mode to the intra prediction unit 206 through theswitch 212. The chroma intra prediction mode calculating unit 225 is acoding information calculating unit that corresponds to the syntaxelement calculating unit 123 relating to the chroma intra predictionmode disposed on the coding side and performs calculation in accordancewith the same semantics rule. In the calculation of the value of thechroma intra prediction mode, the correlation with the luma intraprediction mode of the prediction block of luma signals that is locatedat the same position as the position of the prediction block of chromasignals is used. Thus, in a case where it is determined that a chromaintra prediction mode can be predicted based on the luma intraprediction mode of the prediction block of luma signals that is locatedat the same position as the position of the prediction block of chromasignals on the coding side, the value of the chroma intra predictionmode is predicted based on the value of the luma intra prediction mode.On the other hand, in a case where it is determined that an independentvalue is preferably set to the chroma intra prediction mode rather thanmaking a prediction based on the luma intra prediction mode, a structureis used in which any one of “0” (horizontal direction), “1” (horizontaldirection), “2” (average value), and “3” (inclination of 45 degrees),which are representative intra prediction modes, is set to the chromaintra prediction mode. As a result, the code amount is reduced.

FIG. 14 is a conversion table used for calculating the value of thechroma intra prediction mode based on the value of the syntax elementintra_chroma_pred_mode[x0][y0] and the value of the luma intraprediction mode of the prediction block located at the same position asthe position of the prediction block of chroma signals. By using thisconversion table, the value of the chroma intra prediction mode iscalculated. In addition, as the luma intra prediction mode, a luma intraprediction mode calculated based on the value of the syntax elementrelating to the luma intra prediction mode that has been previouslydecoded in the decoding sequence is referred to. By performing codingand decoding in the coding sequence or the decoding sequence illustratedin FIGS. 17A to 17C, the luma intra prediction mode to be referred tocan be easily specified. As presented in the description of the codingside, in a case where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is “0”, the value of the chroma intraprediction mode is predicted in accordance with the chroma format basedon the value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofchroma signals. In a case where the chroma format is 4:2:0 or 4:4:4, andthe value of the syntax element intra_chroma_pred_mode[x0][y0] is “0”,the value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofchroma signals is directly set as the value of the chroma intraprediction mode. In a case where the chroma format is 4:2:2 and thevalue of the syntax element intra_chroma_pred_mode[x0][y0] is “0”, basedon the conversion table illustrated in FIG. 15, the value of the chromaintra prediction mode is calculated based on the value of the luma intraprediction mode of the prediction block located at the same position asthe position of the prediction block of chroma signals. FIG. 15 is aconversion table used for calculating the value of the chroma intraprediction mode based on the value of the luma intra prediction mode ofthe prediction block located at the same position as the position of theprediction block of chroma signals in a case where the chroma format is4:2:2 that is defined in this example.

In a case where the prediction mode PredMode of the coding block is theinter prediction MODE_INTER, the inter prediction informationcalculating unit 226 calculates the inter prediction information basedon the value of the syntax element relating to the inter predictioninformation in units of prediction blocks and supplies the calculatedvalue of the inter prediction information to the inter prediction unit207 through the switch 212. The inter prediction information calculatingunit 226 is a coding information calculating unit that corresponds tothe syntax element calculating unit 124 relating to the inter predictioninformation disposed on the coding side and performs calculation inaccordance with the same semantics rule. In the calculated interprediction information in units of prediction blocks, information suchas the inter prediction mode (the L0 prediction, the L1 prediction, orboth predictions), an index used for specifying a plurality of referencepictures, and a motion vector is included.

Next, the syntax rule used in this example will be described withfocusing on points relating to the intra prediction mode that is afeature of the embodiment. FIG. 18 is an example of a syntax rule forcoding and decoding coding information in units of coding blocks that isused by the entropy coding unit 126 disposed on the coding side and theentropy decoding unit 222 disposed on the decoding side. FIG. 19 is anexample of a syntax rule used for coding and decoding coding informationof a prediction unit that is used by the entropy coding unit 126disposed on the coding side and the entropy decoding unit 222 disposedon the decoding side.

x0 and y0 illustrated in FIG. 18 are coordinates that represent theposition of the coding block. FIG. 18 illustrates entropy coding orentropy decoding of coding information of one set of prediction unitsthat is performed in accordance with a syntax rule represented in FIG.19 in a case where the partition mode (PartMode) is 2N×2N partition(PART_2N×2N) in units of coding blocks. In addition, entropy coding orentropy decoding of coding information of four sets of prediction unitsis illustrated which is performed in accordance with the syntax ruleillustrated in FIG. 19 in a case where the partition mode (PartMode) isN×N partition (PART_N×N).

FIG. 19 illustrates the syntax rule used for coding coding informationof a prediction unit. x0 and y0 illustrated in FIG. 19 are coordinatesthat represent the positions of a prediction unit of a luma signal and aprediction block. FIG. 19 illustrates the process of the entropy codingor entropy decoding of the syntax element relating to the luma intraprediction mode in units of one set of prediction blocks, which isperformed in units of prediction blocks in a case where the predictionmode PredMode is the intra prediction (MODE_INTRA). In a case where theprediction mode (PredMode) is the intra prediction MODE_INTRA, entropycoding or entropy decoding of the syntax elementprev_intra_luma_pred_flag[x0][y0] is performed. On the other hand, in acase where the syntax element prev_intra_luma_pred_flag[x0][y0] is “1”(true), entropy coding or entropy decoding of the syntax elementmpm_idx[x0][y0] is performed. In a case where the syntax elementprev_intra_luma_pred_flag[x0][y0] is “0” (false), entropy coding orentropy decoding of the syntax element rem_intra_luma_pred_mode[x0][y0]is performed.

In addition, entropy coding or entropy decoding of a syntax elementintra_chroma_pred_mode[x0][y0] relating to a chroma intra predictionmode that is performed in accordance with a chroma format and apartition index PartIdx is illustrated. The chroma formatChromaArrayType is a variable that represents the chroma format, “0”represents monochrome (basically, although a mode in which luma signalsand chroma signals are independently coded at 4:4:4 is included, such acase is regarded as the monochrome in this example), “1” represents4:2:0, “2” represents 4:2:2, and “3” represents 4:4:4.

In a case where any one of a condition where the chroma format is 4:2:0,4:2:2, or 4:4:4 (ChromaArrayType is not “0”) and the partition indexPartIdx is “0”, a condition where the chroma format is 4:2:2(ChromaArrayType is “2”) and the partition index PartIdx is “2”, and acondition where the chroma format is 4:4:4 (ChromaArrayType is “3”) issatisfied, entropy coding or entropy decoding of a syntax elementintra_chroma_pred_mode[x0][y0] relating to the chroma intra predictionmode performed in units of prediction blocks is illustrated. In otherwords, in a case where the chroma format is 4:2:0, only in a case wherethe partition index PartIdx is “0”, entropy coding or entropy decodingof a syntax element relating to the chroma intra prediction mode having“0” as the partition index PartIdx is performed right after the syntaxelement relating to the luma intra prediction mode. In addition, in acase where the chroma format is 4:2:2, only in a case where thepartition index PartIdx is “0” or “2”, right after the syntax elementrelating to the luma intra prediction mode, entropy coding or entropydecoding of a syntax element relating to the chroma intra predictionmode of the same partition index PartIdx is performed, and, in a casewhere the chroma format is “4:4:4”, in a case where the partition indexPartIdx is any one of 0, 1, 2, and 3, right after the syntax elementrelating to the luma intra prediction mode, entropy coding or entropydecoding of a syntax element relating to the chroma intra predictionmode of the same partition index PartIdx is illustrated. Furthermore,the case of 2N×2N partition (PART_2N×2N) corresponds to a case where thepartition index PartIdx is “0”, right after the syntax element relatingto the luma intra prediction mode, entropy coding or entropy decoding ofa syntax element relating to the chroma intra prediction mode having “0”as the partition index PartIdx is performed.

Next, the processing sequence of the coding process of codinginformation in units of coding blocks and prediction blocks that isperformed by the second bitstream constructing unit 113 illustrated inFIG. 1 will be described with focusing on points relating to the intraprediction mode that is a feature of the embodiment. FIG. 20 is aflowchart that illustrates the processing sequence of the coding processin units of coding blocks and prediction blocks that is performed by thesecond bitstream constructing unit 113 illustrated in FIG. 1.

First, on the coding side, the value of the syntax element relating tocoding information including the prediction mode of the coding block,the partition mode, and the like is calculated by the syntax elementcalculating unit 121 relating to the coding information in units ofcoding blocks, and entropy coding of the calculated value of the syntaxelement is performed by the entropy coding unit 126 in step S1001.Subsequently, in a case where the prediction mode PredMode of the codingblock is not the intra prediction MODE_INTRA (No in step S1002), theprocess proceeds to step S1017, the value of the syntax element relatingto inter information is calculated for each prediction block inaccordance with the partition mode by the syntax element calculatingunit 124 relating to the inter prediction information, entropy coding ofthe calculated value of the syntax element is performed by the entropycoding unit 126 in step S1017, and this coding process ends. In a casewhere the prediction mode PredMode of the coding block is the intraprediction MODE_INTRA (Yes in step S1002), the process proceeds to acoding process of the intra prediction mode of step S1003 and subsequentsteps.

Subsequently, in a case where the prediction mode of the coding block isthe intra prediction, a coding process of the luma intra prediction modeof the prediction block, of which the partition index PartIdx is “0”, ofluma signals is performed by the syntax element calculating unit 122relating to the luma intra prediction mode and the entropy coding unit126 in step S1003.

Here, the sequence of the coding process of the luma intra predictionmode of the prediction block of luma signals, which is performed by thesyntax element calculating unit 122 relating to the luma intraprediction mode and the entropy coding unit 126, will be described byreferring to a flowchart illustrated in FIG. 21. FIG. 21 is a flowchartthat illustrates the sequence of the coding process of the luma intraprediction mode of the prediction block of luma signals, which isperformed by the syntax element calculating unit 122 relating to theluma intra prediction mode and the entropy coding unit 126. First, thevalue of each syntax element relating to the luma intra prediction modeof the prediction block of luma signals is calculated by the syntaxelement calculating unit 122 relating to the luma intra prediction modein step S1101. At this time, the value of the luma intra prediction modeis compared with the luma intra prediction mode of a neighboring block.In a case where a prediction block having the same value is present, thevalue of the syntax element prev_intra_luma_pred_flag[x0][y0] is setto“1” (true), and a value used for specifying a reference destination isset to the syntax element mpm_idx[x0][y0] that is an index indicatingthe prediction block of a prediction source. On the other hand, in acase where there is no prediction block having the same value, the valueof the syntax element prev_intra_luma_pred_flag[x0][y0] is set to “0”(false), and a value used for specifying the luma intra prediction modeis set to the syntax element rem_intra_luma_pred_mode[x0][y0] thatrepresents the luma intra prediction mode. Subsequently, entropy codingof the value of each syntax element relating to the luma intraprediction mode of the prediction block of luma signals is performed bythe entropy coding unit 126 in step S1102, and this coding process ends.The sequence of the coding process illustrated in FIG. 21 is thesequence of a common coding process that is used not only in step S1003illustrated in FIG. 20 but also in steps S1007, S1010, and S1013.

Again, referring back to FIG. 20, subsequently, in a case where thechroma format is 4:2:0, 4:2:2, or 4:4:4 (Yes in step S1004), a codingprocess of the chroma intra prediction mode of a prediction block ofwhich the partition index PartIdx of the chroma signal is “0” isperformed by the syntax element calculating unit 123 relating to thechroma intra prediction mode and the entropy coding unit 126 in stepS1005. On the other hand, in a case where the chroma format is not anyone of 4:2:0, 4:2:2, and 4:4:4, in other words, in a case where thechroma format is monochrome (No in step S1004), since there is noprediction block of a chroma signal, step S1005 is skipped, and theprocess proceeds to the next step S1006.

Here, the sequence of the coding process of the chroma intra predictionmode of a prediction block of a chroma signal that is performed by thesyntax element calculating unit 123 relating to the chroma intraprediction mode and the entropy coding unit 126 will be described withreference to a flowchart represented in FIG. 22. FIG. 22 is a flowchartthat represents the sequence of a coding process of a chroma intraprediction mode of a prediction block of a chroma signal that isperformed by the syntax element calculating unit 123 relating to thechroma intra prediction mode and the entropy coding unit 126. First, thevalue of each syntax element relating to the chroma intra predictionmode of a prediction block of a chroma signal is calculated by thesyntax element calculating unit 123 relating to the chroma intraprediction mode in step S1201. At this time, the value of the syntaxelement intra_chroma_pred_mode[x0][y0] relating to the chroma intraprediction mode is calculated by using the conversion table illustratedin FIG. 16 based on the value of the chroma intra prediction mode andthe value of a luma intra prediction mode of a prediction block that islocated at the same position as the position of the prediction block ofthe chroma signal. Subsequently, entropy coding of the value of eachsyntax element relating to the chroma intra prediction mode of theprediction block of the chroma signal is performed by the entropy codingunit 126 in step S1202, and the coding process ends. Here, the sequenceof the coding process illustrated in FIG. 22 is the sequence of a codingprocess that is commonly used also in steps S1009, S1012, and S1015 inaddition to step S1005 illustrated in FIG. 20.

Again, referring back to FIG. 20, subsequently, in a case where thepartition mode of the coding block is not the N×N partition, in otherwords, in a case where the partition mode is 2N×2N (No in step S1006),there is only a prediction block having “0” as the partition indexPartIdx, and there is no intra prediction mode to be further coded.Accordingly, this coding process ends.

On the other hand, in a case where the partition mode of the codingblock is the N×N partition (Yes in step S1006), the process proceeds tothe coding process of an intra prediction mode of a prediction block ofwhich the partition index PartIdx is more than “0”. First, a codingprocess of the luma intra prediction mode of a prediction block of whichthe partition index PartIdx of the luma signal is “1” is performed inaccordance with the sequence of the coding process illustrated in FIG.21 in step S1007. Subsequently, in a case where the chroma format is4:4:4 (Yes in step S1008), a coding process of the chroma intraprediction mode of a prediction block of which the partition indexPartIdx of the chroma signal is “1” is performed in accordance with thesequence of the coding process illustrated in FIG. 22 in step S1009. Onthe other hand, in a case where the chroma format is not 4:4:4, in otherwords, in a case where the chroma format is 4:2:0, 4:2:2, or monochrome(No in step S1008), since there is no prediction block of which thepartition index PartIdx of the chroma signal is “1”, step S1009 isskipped, and the process proceeds to the next step S1010.

Subsequently, a coding process of the luma intra prediction mode of aprediction block of which the partition index PartIdx of the luma signalis “2” is performed in accordance with the sequence of the codingprocess illustrated in FIG. 21 in step S1010. Subsequently, in a casewhere the chroma format is 4:2:2 or 4:4:4 (Yes in step S1011), a codingprocess of the chroma intra prediction mode of a prediction block ofwhich the partition index PartIdx of the chroma signal is “2” isperformed in accordance with the sequence of the coding processillustrated in FIG. 22 in step S1012. On the other hand, in a case wherethe chroma format is neither 4:2:2 nor 4:4:4, in other words, in a casewhere the chroma format is 4:2:0 or monochrome (No in step S1011), sincethere is no prediction block of which the partition index PartIdx of thechroma signal is “2”, step S1012 is skipped, and the process proceeds tothe next step S1013.

Subsequently, a coding process of the luma intra prediction mode of aprediction block of which the partition index PartIdx of the luma signalis “3” is performed in accordance with the sequence of the codingprocess illustrated in FIG. 21 in step S1013. Subsequently, in a casewhere the chroma format is 4:4:4 (Yes in step S1014), a coding processof the chroma intra prediction mode of a prediction block of which thepartition index PartIdx of the chroma signal is “3” is performed inaccordance with the sequence of the coding process illustrated in FIG.22 in step S1015. On the other hand, in a case where the chroma formatis other than 4:4:4, in other words, in a case where the chroma formatis 4:2:0, 4:2:2, or monochrome (No in step S1014), since there is noprediction block of which the partition index PartIdx of the chromasignal is “3”, step S1015 is skipped, and the coding process ends.

According to this coding process, in accordance with the sequenceillustrated in FIGS. 17A to 17C, the luma intra prediction mode and thechroma intra prediction mode belonging to a same prediction unit areconsecutively coded, and, when the chroma intra prediction mode iscalculated on the decoding side, the calculation process is performed byreferring to the luma intra prediction mode that has been previouslydecoded and calculated. Accordingly, by referring to the luma intraprediction mode, the decoding process of the chroma intra predictionmode can be performed at optimal timing while the coding efficiency ofthe chroma intra prediction mode is increased.

Next, the processing sequence of the decoding process of codinginformation in units of coding blocks and prediction blocks that isperformed by the second bitstream decoding unit 203 illustrated in FIG.2 will be described with focusing on points relating to the intraprediction mode that is a feature of the embodiment. FIG. 23 is aflowchart that illustrates the processing sequence of the decodingprocess in units of coding blocks and prediction blocks that isperformed by the second bitstream decoding unit 203 illustrated in FIG.2.

First, on the decoding side, the value of the syntax element relating tocoding information including the prediction mode of the coding block,the partition mode, and the like is derived by performing entropydecoding the bitstream using the entropy decoding unit 222 in stepS2001, and the value of the coding information including the predictionmode of the coding block, the partition mode, and the like is calculatedbased on the value of each syntax element decoded by the codinginformation calculating unit 223 in units of coding blocks.Subsequently, in a case where the prediction mode PredMode of the codingblock is not the intra prediction MODE_INTRA (No in step S2002), theprocess proceeds to step S2016, the value of the syntax element relatingto inter information is acquired for each prediction block in accordancewith the partition mode by performing entropy decoding using the entropydecoding unit 222, the value of the inter information is calculated foreach prediction block in accordance with the partition mode by the interprediction information calculating unit 226 in step S2016, and thisdecoding process ends. In a case where the prediction mode PredMode ofthe coding block is the intra prediction MODE_INTRA (Yes in step S2002),the process proceeds to a decoding process of the intra prediction modeof step S2003 and subsequent steps.

Subsequently, in a case where the prediction mode of the coding block isthe intra prediction, a decoding process of the luma intra predictionmode of the prediction block, of which the partition index PartIdx of is“0”, of luma signals is performed by the entropy decoding unit 222 andthe luma intra prediction mode calculating unit 224 in step S2003.

Here, the sequence of the decoding process of the luma intra predictionmode of the prediction block of luma signals, which is performed by theentropy decoding unit 222 and the luma intra prediction mode calculatingunit 224, will be described by referring to a flowchart illustrated inFIG. 24. FIG. 24 is a flowchart that illustrates the sequence of thedecoding process of the luma intra prediction mode of the predictionblock of luma signals, which is performed by the entropy decoding unit222 and the luma intra prediction mode calculating unit 224. First,entropy decoding of the bitstream is performed by the entropy decodingunit 222, whereby the value of each syntax element relating to the lumaintra prediction mode of the prediction block of luma signals is derivedin step S2101. Subsequently, the value of the luma intra prediction modeof the prediction block of luma signals is calculated based on the valueof each decoded syntax element decoded in step S2101 by the luma intraprediction mode calculating unit 224 of the luma intra prediction modein step S2102. At this time, in a case where the value of the syntaxelement prev_intra_luma_pred_flag[x0][y0] is “1” (true), the luma intraprediction mode of the neighboring prediction block indicated by thesyntax element mpm_idx[x0][y0] that is an index indicating theprediction block of a prediction source is set as the luma intraprediction mode of the prediction mode. On the other hand, in a casewhere the value of the syntax element prev_intra_luma_pred_flag[x0][y0]is “0” (false), the luma intra prediction mode is calculated based onthe value of the syntax element rem_intra_luma_pred_mode[x0][y0] thatrepresents the luma intra prediction mode, and this decoding processends. The sequence of the decoding process illustrated in FIG. 24 is thesequence of a common decoding process that is used not only in stepS2003 illustrated in FIG. 23 but also in steps S2007, S2010, and S2013.

Again, referring back to FIG. 23, subsequently, in a case where thechroma format is 4:2:0, 4:2:2, or 4:4:4 (Yes in step S2004), thedecoding process of the chroma intra prediction mode of the predictionblock, of which the partition index PartIdx is “0”, of chroma signals isperformed by the entropy decoding unit 222 and the chroma intraprediction mode calculating unit 225 in step S2005. In addition, in acase where the chroma format is not any one of 4:2:0, 4:2:2, and 4:4:4,in other words, in a case where the chroma format is monochrome (No instep S2004), since there is no prediction block of a chroma signal, stepS2005 is skipped, and the process proceeds to the next step S2006.

Here, the sequence of the decoding process of the chroma intraprediction mode of the prediction block of chroma signals that isperformed by the entropy decoding unit 222 and the chroma intraprediction mode calculating unit 225 will be described by referring to aflowchart illustrated in FIG. 25. FIG. 25 is a flowchart thatillustrates the sequence of the decoding process of the chroma intraprediction mode of the prediction block of chroma signals, which isperformed by the entropy decoding unit 222 and the chroma intraprediction mode calculating unit 225. First, the value of the syntaxelement intra_chroma_pred_mode[x0][y0] relating to the chroma intraprediction mode of the prediction block of chroma signals is calculatedby performing entropy decoding the bitstream using the entropy decodingunit 222 in step S2201. Subsequently, the value of the chroma intraprediction mode of the prediction block of chroma signals is calculatedby the chroma intra prediction mode calculating unit 225 in step S2202.Here, the sequence of the process of calculating the chroma intraprediction mode of the prediction block of chroma signals that isperformed by the chroma intra prediction mode calculating unit 225 willbe described by referring to a flowchart illustrated in FIG. 26. FIG. 26is a flowchart that illustrates the sequence of the process ofcalculating the chroma intra prediction mode that is performed in stepS2202 illustrated in FIG. 25. First, it is determined whether or not thevalue of the syntax element intra_chroma_pred_mode[x0][y0] relating tothe chroma intra prediction mode of the prediction block of chromasignals is “0” in step S2301. In a case where the value of the syntaxelement is “0” (Yes in step S2301), the process proceeds to step S2302.In a case where the chroma format is 4:2:0 or 4:4:4 (Yes in step S2302),the value of the luma intra prediction mode of the prediction blocklocated at the same position as the position of the prediction block ofchroma signals is directly set as the value of the chroma intraprediction mode in step S2303, and this calculation process ends. On theother hand, in a case where the chroma format is 4:2:0 or 4:4:4, inother words, in the case of 4:2:2 (No in step S2302), by using theconversion table illustrated in FIG. 15, the value of the chroma intraprediction mode is calculated based on the value of a luma intraprediction mode of a prediction block that is located at the sameposition as the position of the prediction block of the chroma signal(step S2304), and this calculation process ends. On the other hand, in acase where the value of the syntax elementintra_chroma_pred_mode[x0][y0] is other than“0” (No in step S2301), byusing the conversion table illustrated in FIG. 14, the value of the lumaintra prediction mode is converted into the value of the chroma intraprediction mode in step S2305, and this calculation process ends. Atthis time, based on the value of the syntax elementintra_chroma_pred_mode[x0][y0] relating to the chroma intra predictionmode decoded in step S2201 and the value of the luma intra predictionmode of a prediction block located at the same position as the positionof the prediction block of the chroma signal, in other words, based onthe value of the luma intra prediction mode calculated in the lateststep, by using the conversion table illustrated in FIG. 14, the value ofthe syntax element is calculated, and this decoding process ends. Thesequence of the decoding process illustrated in FIG. 25 is the sequenceof a common decoding process that is used not only in step S2005illustrated in FIG. 23 but also in steps S2009, S2012, and S2015.

Again, referring back to FIG. 23, subsequently, in a case where thepartition mode of the coding block is not the N×N partition, in otherwords, in a case where the partition mode is 2N×2N (No in step S2006),since there is only a prediction block of which the partition indexPartIdx is “0”, and there is no intra prediction mode to be furtherdecoded, this decoding process ends.

On the other hand, in a case where the partition mode of the codingblock is the N×N partition (Yes in step S2006), the process proceeds toa decoding process of the intra prediction mode of a prediction block ofwhich the partition index PartIdx is more than “0”. First, in accordancewith the sequence of the decoding process illustrated in FIG. 24, adecoding process of the luma intra prediction mode of a prediction blockof which the partition index PartIdx of the luma signal is “1” isperformed in step S2007. Subsequently, in a case where the chroma formatis 4:4:4 (Yes in step S2008), in accordance with the processing sequenceillustrated in FIG. 25, a decoding process of the chroma intraprediction mode of a prediction block of which the partition indexPartIdx of the chroma signal is “1” is performed in step S2009. On theother hand, in a case where the chroma format is not 4:4:4, in otherwords, the chroma format is 4:2:0, 4:2:2, or monochrome (No in stepS2008), since there is no prediction block of which the partition indexPartIdx of the chroma signal is “1”, step S2009 is skipped, and theprocess proceeds to the next step S2010.

Subsequently, in accordance with the processing sequence illustrated inFIG. 24, a decoding process of the luma intra prediction mode of aprediction block of which the partition index PartIdx of the luma signalis “2” is performed in step S2010. Subsequently, in a case where thechroma format is 4:2:2 or 4:4:4 (Yes in step S2011), in accordance withthe processing sequence illustrated in FIG. 25, a decoding process ofthe chroma intra prediction mode of a prediction block of which thepartition index PartIdx of the chroma signal is “2” is performed in stepS2012. On the other hand, in a case where the chroma format is neither4:2:2 nor 4:4:4, in other words, the chroma format is 4:2:0 ormonochrome (No in step S2011), since there is no prediction block ofwhich the partition index PartIdx of the chroma signal is “2”, stepS2012 is skipped, and the process proceeds to the next step S2013.

Subsequently, in accordance with the processing sequence illustrated inFIG. 24, a decoding process of the luma intra prediction mode of aprediction block of which the partition index PartIdx of the luma signalis “3” is performed in step S2013. Subsequently, in a case where thechroma format is 4:4:4 (Yes in step S2014), in accordance with theprocessing sequence illustrated in FIG. 25, a decoding process of thechroma intra prediction mode of a prediction block of which thepartition index PartIdx of the chroma signal is “3” is performed in stepS2015. On the other hand, in a case where the chroma format is otherthan 4:4:4, in other words, the chroma format is 4:2:0, 4:2:2, ormonochrome (No in step S2014), since there is no prediction block ofwhich the partition index PartIdx of the chroma signal is “3”, stepS2015 is skipped, and this decoding process ends.

According to this decoding process, in accordance with the sequenceillustrated in FIGS. 17A to 17C, the luma intra prediction mode and thechroma intra prediction mode belonging to a same prediction unit areconsecutively decoded, and, when the chroma intra prediction mode iscalculated, the calculation process is performed by referring to theluma intra prediction mode that has been previously decoded andcalculated. Accordingly, by referring to the luma intra prediction mode,the decoding process of the chroma intra prediction mode can beperformed at optimal timing while the coding efficiency of the chromaintra prediction mode is increased.

A bitstream of a moving picture output by the moving picture codingdevice according to the embodiment described above has a specific dataformat such that the bitstream can be decoded in accordance with thecoding method used in the embodiment, and the moving picture decodingdevice corresponding to the moving picture coding device can decode thebitstream having this specific data format.

In a case where a wired or wireless network is used so as to allow thebitstream to be transmitted and received between the moving picturecoding device and the moving picture decoding device, the bitstream maybe converted to a data format that is appropriate to the transmittingform of the transmitting path and be transmitted. In such a case, amoving picture transmitting device that converts the bitstream output bythe moving picture coding device into coding data of a data format thatis appropriate to the transmitting form of the transmitting path andtransmits the coding data to the network and a moving picture receivingdevice that receives the coding data from the network, restores abitstream from the coding data, and supplies the restored bitstream tothe moving picture decoding device are disposed.

The moving picture transmitting device includes: a memory that buffers abitstream output by the moving picture coding device; a packetprocessing unit that packetizes the bitstream; and a transmitting unitthat transmits the packetized coding data through a network. The movingpicture receiving device includes: a receiving unit that receivespacketized coding data through a network; a memory that buffers thereceived coding data; and a packet processing unit that constructs abitstream by performing a packet process of the coding data and suppliesthe bitstream to the moving picture decoding device.

The above-described processes relating to coding and decoding may berealized not only as transmitting/storage/receiving devices usinghardware but also by firmware stored in a read only memory (ROM), aflash memory, or the like or software for a computer or the like. Thefirmware program and the software program may be provided with beingrecorded in a computer-readable recording medium, be provided from aserver through a wired or wireless network, or be provided as databroadcasting of a terrestrial or satellite digital broadcasts.

As above, the embodiment of the present invention has been described.However, the embodiment is merely an example, and it should beunderstood by those skilled in the art that various changes andmodifications may be made in each constituent element and thecombination of the processes, and such changes and modifications belongto the scope of the present invention.

[Item 1]

A picture coding device that performs intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and codes information relating to an intra prediction mode, thepicture coding device including an intra prediction unit that, when anintra prediction of the picture signal is made in units of codingblocks, in a case where a chroma format is 4:2:2, in a mode for settinga chroma intra prediction mode in accordance with a luma intraprediction mode, sets a chroma intra prediction mode based on the lumaintra prediction mode and the chroma format and makes an intraprediction of the chroma signal.

[Item 2]

The picture coding device described in Item 1, wherein, in a case wherethe chroma format is 4:2:2, in the mode for setting the chroma intraprediction mode in accordance with the luma intra prediction mode, theintra prediction unit sets the chroma intra prediction mode having aprediction direction acquired by converting a prediction direction ofthe luma intra prediction mode into a direction according to the chromaformat and makes the intra prediction of the chroma signal.

[Item 3]

A picture coding device that performs intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and codes information relating to an intra prediction mode, thepicture coding device including:

an intra prediction unit that, when an intra prediction of the picturesignal is made in units of minimal coding blocks set in advance, in acase where a partition mode in which the luma signal is partitionedhorizontally and vertically is set, makes an intra prediction of thechroma signal in units of prediction blocks of the intra prediction ofthe chroma signal within the minimal coding block set in accordance witha chroma format; and

a bitstream constructing unit that constructs a bitstream in whichinformation relating to a luma intra prediction mode of the predictionblock of the luma signal and information relating to a chroma intraprediction mode of the prediction block of the chroma signal located ata reference position that is the same as the position of the predictionblock of the luma signal are continuous.

[Item 4]

A picture coding device that performs intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and codes information relating to an intra prediction mode, thepicture coding device including:

a luma signal intra prediction unit that, when an intra prediction ofthe picture signal is made in units of minimal coding blocks set inadvance, in a case where a partition mode in which the luma signal ispartitioned horizontally and vertically is set, sets prediction blocksof first to fourth luma signals acquired by partitioning the luma signalof the minimal coding block horizontally and vertically and predicts aluma signal based on neighboring blocks of coded luma signals inaccordance with a luma intra prediction mode for each prediction blockof the luma signal;

a chroma signal intra prediction unit that, in a case where thepartition mode is set, and a chroma format is 4:4:4, sets predictionblocks of first to fourth chroma signals acquired by partitioning thechroma signal of the minimal coding block horizontally and verticallyand predicts the chroma signal based on neighboring blocks of codedchroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signal; and

a bitstream constructing unit that constructs a bitstream by codinginformation relating to the prediction mode of the minimal coding block,

wherein the chroma signal intra prediction unit, in a case where thechroma format is 4:4:4, in a mode for setting the chroma intraprediction mode in accordance with the luma intra prediction mode, setschroma intra prediction modes of the prediction blocks of first, second,third, and fourth chroma signals by using values representing the lumaintra prediction modes of the prediction blocks of the first, second,third, and fourth luma signals within the minimal coding block as valuesrepresenting the chroma intra prediction modes of the prediction blocksof the first, second, third, and fourth chroma signals within theminimal coding block that are located at respective same referencepositions.

[Item 5]

The picture coding device described in Item 4, wherein, in a case wherethe chroma format is 4:4:4, the bitstream constructing unit constructs abitstream in which information relating to the prediction modes isarranged in an order of, within the minimal coding block, the luma intraprediction mode of the prediction block of the first luma signal, thechroma intra prediction mode of the prediction block of the first chromasignal located at a reference position that is the same as the positionof the prediction block of the first luma signal, the luma intraprediction mode of the prediction block of the second luma signal, thechroma intra prediction mode of the prediction block of the secondchroma signal located at a reference position that is the same as theposition of the prediction block of the second luma signal, the lumaintra prediction mode of the prediction block of the third luma signal,the chroma intra prediction mode of the prediction block of the thirdchroma signal located at a reference position that is the same as theposition of the prediction block of the third luma signal, the lumaintra prediction mode of the prediction block of the fourth luma signal,and the chroma intra prediction mode of the prediction block of thefourth chroma signal located at a reference position that is the same asthe position of the prediction block of the fourth luma signal.

[Item 6]

There is provided a picture coding device that performs intra predictioncoding of a picture signal including a luma signal and a chroma signalin units of blocks and codes information relating to an intra predictionmode, the picture coding device including:

a luma signal intra prediction unit that, when an intra prediction ofthe picture signal is made in units of minimal coding blocks set inadvance, in a case where a partition mode in which the luma signal ispartitioned horizontally and vertically is set, sets prediction blocksof first to fourth luma signals acquired by partitioning the luma signalof the minimal coding block horizontally and vertically and predicts aluma signal based on neighboring blocks of coded luma signals inaccordance with a luma intra prediction mode for each prediction blockof the luma signal;

a chroma signal intra prediction unit that, in a case where thepartition mode is set, and a chroma format is 4:2:2, sets predictionblocks of first and second chroma signals acquired by horizontallypartitioning the chroma signal of the minimal coding block and predictsthe chroma signal based on neighboring blocks of coded chroma signals inaccordance with a chroma intra prediction mode for each prediction blockof the chroma signal; and

a bitstream constructing unit that constructs a bitstream by codinginformation relating to the prediction mode of the minimal coding block,

wherein the chroma signal intra prediction unit, in a case where thechroma format is 4:2:2, in a mode for setting the chroma intraprediction mode in accordance with the luma intra prediction mode, setschroma intra prediction modes of the prediction blocks of the first andsecond chroma signals by converting values representing the luma intraprediction modes of the prediction blocks of the first and third lumasignals within the minimal coding block into values representing thechroma intra prediction modes of the prediction blocks of the first andsecond chroma signals within the minimal coding block that are locatedat respective same reference positions in accordance with a conversionrule set in advance.

[Item 7]

The picture coding device described in Item 6, wherein, in a case wherethe chroma format is 4:2:2, the bitstream constructing unit constructs abitstream in which information relating to the prediction modes isarranged in an order of, within the minimal coding block, the luma intraprediction mode of the prediction block of the first luma signal, thechroma intra prediction mode of the prediction block of the first chromasignal located at a reference position that is the same as the positionof the prediction block of the first luma signal, the luma intraprediction mode of the prediction block of the second luma signal, theluma intra prediction mode of the prediction block of the third lumasignal, the chroma intra prediction mode of the prediction block of thesecond chroma signal located at a reference position that is the same asthe position of the prediction block of the third luma signal, and theluma intra prediction mode of the prediction block of the fourth lumasignal.

[Item 8]

A picture coding method for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding method including, when an intra prediction of the picturesignal is made in units of coding blocks, in a case where a chromaformat is 4:2:2, in a mode for setting a chroma intra prediction mode inaccordance with a luma intra prediction mode, setting a chroma intraprediction mode based on the luma intra prediction mode and the chromaformat and making an intra prediction of the chroma signal.

[Item 9]

A picture coding method for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding method including:

when an intra prediction of the picture signal is made in units ofminimal coding blocks set in advance, in a case where a partition modein which the luma signal is partitioned horizontally and vertically isset, making an intra prediction of the chroma signal in units ofprediction blocks of the intra prediction of the chroma signal withinthe minimal coding block set in accordance with a chroma format; and

constructing a bitstream in which information relating to a luma intraprediction mode of the prediction block of the luma signal andinformation relating to a chroma intra prediction mode of the predictionblock of the chroma signal located at a reference position that is thesame as the position of the prediction block of the luma signal arecontinuous.

[Item 10]

A picture coding method for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding method including:

when an intra prediction of the picture signal is made in units ofminimal coding blocks set in advance, in a case where a partition modein which the luma signal is partitioned horizontally and vertically isset, setting prediction blocks of first to fourth luma signals acquiredby partitioning the luma signal of the minimal coding block horizontallyand vertically and predicting a luma signal based on neighboring blocksof coded luma signals in accordance with a luma intra prediction modefor each prediction block of the luma signal;

in a case where the partition mode is set, and a chroma format is 4:4:4,setting prediction blocks of first to fourth chroma signals acquired bypartitioning the chroma signal of the minimal coding block horizontallyand vertically and predicting the chroma signal based on neighboringblocks of coded chroma signals in accordance with a chroma intraprediction mode for each prediction block of the chroma signal; and

constructing a bitstream by coding information relating to theprediction mode of the minimal coding block,

wherein, in the setting of prediction blocks and predicting of thechroma signal, in a case where the chroma format is 4:4:4, in a mode forsetting the chroma intra prediction mode in accordance with the lumaintra prediction mode, chroma intra prediction modes of the predictionblocks of first, second, third, and fourth chroma signals are set byusing values representing the luma intra prediction modes of theprediction blocks of the first, second, third, and fourth luma signalswithin the minimal coding block as values representing the chroma intraprediction modes of the prediction blocks of the first, second, third,and fourth chroma signals within the minimal coding block that arelocated at respective same reference positions.

[Item 11]

A picture coding method for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding method including:

when an intra prediction of the picture signal is made in units ofminimal coding blocks set in advance, in a case where a partition modein which the luma signal is partitioned horizontally and vertically isset, setting prediction blocks of first to fourth luma signals acquiredby partitioning the luma signal of the minimal coding block horizontallyand vertically and predicting a luma signal based on neighboring blocksof coded luma signals in accordance with a luma intra prediction modefor each prediction block of the luma signal;

in a case where the partition mode is set, and a chroma format is 4:2:2,setting prediction blocks of first and second chroma signals acquired byhorizontally partitioning the chroma signal of the minimal coding blockand predicting the chroma signal based on neighboring blocks of codedchroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signal; and

constructing a bitstream by coding information relating to theprediction mode of the minimal coding block,

wherein, in the setting of prediction blocks and predicting of thechroma signal, in a case where the chroma format is 4:2:2, in a mode forsetting the chroma intra prediction mode in accordance with the lumaintra prediction mode, chroma intra prediction modes of the predictionblocks of the first and second chroma signals are set by convertingvalues representing the luma intra prediction modes of the predictionblocks of the first and third luma signals within the minimal codingblock into values representing the chroma intra prediction modes of theprediction blocks of the first and second chroma signals within theminimal coding block that are located at respective same referencepositions in accordance with a conversion rule set in advance.

[Item 12]

A picture coding program for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding program causing a computer to execute, when an intraprediction of the picture signal is made in units of coding blocks, in acase where a chroma format is 4:2:2, in a mode for setting a chromaintra prediction mode in accordance with a luma intra prediction mode,setting a chroma intra prediction mode based on the luma intraprediction mode and the chroma format and making an intra prediction ofthe chroma signal.

[Item 13]

A picture coding program for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding program causing a computer to execute:

-   -   when an intra prediction of the picture signal is made in units        of minimal coding blocks set in advance, in a case where a        partition mode in which the luma signal is partitioned        horizontally and vertically is set, making an intra prediction        of the chroma signal in units of prediction blocks of the intra        prediction of the chroma signal within the minimal coding block        set in accordance with a chroma format; and

constructing a bitstream in which information relating to a luma intraprediction mode of the prediction block of the luma signal andinformation relating to a chroma intra prediction mode of the predictionblock of the chroma signal located at a reference position that is thesame as the position of the prediction block of the luma signal arecontinuous.

[Item 14]

A picture coding program for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding program causing a computer to execute:

when an intra prediction of the picture signal is made in units ofminimal coding blocks set in advance, in a case where a partition modein which the luma signal is partitioned horizontally and vertically isset, setting prediction blocks of first to fourth luma signals acquiredby partitioning the luma signal of the minimal coding block horizontallyand vertically and predicting a luma signal based on neighboring blocksof coded luma signals in accordance with a luma intra prediction modefor each prediction block of the luma signal;

-   -   in a case where the partition mode is set, and a chroma format        is 4:4:4, setting prediction blocks of first to fourth chroma        signals acquired by partitioning the chroma signal of the        minimal coding block horizontally and vertically and predicting        the chroma signal based on neighboring blocks of coded chroma        signals in accordance with a chroma intra prediction mode for        each prediction block of the chroma signal; and

constructing a bitstream by coding information relating to theprediction mode of the minimal coding block,

wherein, in the setting of prediction blocks and predicting of thechroma signal, in a case where the chroma format is 4:4:4, in a mode forsetting the chroma intra prediction mode in accordance with the lumaintra prediction mode, chroma intra prediction modes of the predictionblocks of first, second, third, and fourth chroma signals are set byusing values representing the luma intra prediction modes of theprediction blocks of the first, second, third, and fourth luma signalswithin the minimal coding block as values representing the chroma intraprediction modes of the prediction blocks of the first, second, third,and fourth chroma signals within the minimal coding block that arelocated at respective same reference positions.

[Item 15]

A picture coding program for performing intra prediction coding of apicture signal including a luma signal and a chroma signal in units ofblocks and coding information relating to an intra prediction mode, thepicture coding program causing a computer to execute:

when an intra prediction of the picture signal is made in units ofminimal coding blocks set in advance, in a case where a partition modein which the luma signal is partitioned horizontally and vertically isset, setting prediction blocks of first to fourth luma signals acquiredby partitioning the luma signal of the minimal coding block horizontallyand vertically and predicting a luma signal based on neighboring blocksof coded luma signals in accordance with a luma intra prediction modefor each prediction block of the luma signal;

in a case where the partition mode is set, and a chroma format is 4:2:2,setting prediction blocks of first and second chroma signals acquired byhorizontally partitioning the chroma signal of the minimal coding blockand predicting the chroma signal based on neighboring blocks of codedchroma signals in accordance with a chroma intra prediction mode foreach prediction block of the chroma signal; and

constructing a bitstream by coding information relating to theprediction mode of the minimal coding block,

wherein, in the setting of prediction blocks and predicting of thechroma signal, in a case where the chroma format is 4:2:2, in a mode forsetting the chroma intra prediction mode in accordance with the lumaintra prediction mode, chroma intra prediction modes of the predictionblocks of the first and second chroma signals are set by convertingvalues representing the luma intra prediction modes of the predictionblocks of the first and third luma signals within the minimal codingblock into values representing the chroma intra prediction modes of theprediction blocks of the first and second chroma signals within theminimal coding block that are located at respective same referencepositions in accordance with a conversion rule set in advance.

[Item 16]

A picture decoding device that performs intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding device including: an intra prediction unit that, whenan intra prediction of the picture signal is made in units of codingblocks, in a case where a chroma format is 4:2:2, in a mode for settinga chroma intra prediction mode in accordance with a luma intraprediction mode, sets a chroma intra prediction mode based on the lumaintra prediction mode and the chroma format and makes an intraprediction of the chroma signal.

[Item 17]

The picture decoding device described in Item 16, wherein, in a casewhere the chroma format is 4:2:2, in the mode for setting the chromaintra prediction mode in accordance with the luma intra prediction mode,the intra prediction unit sets the chroma intra prediction mode having aprediction direction acquired by converting a prediction direction ofthe luma intra prediction mode into a direction according to the chromaformat and makes the intra prediction of the chroma signal.

[Item 18]

A picture decoding device that performs intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding device including:

a bitstream decoding unit that consecutively decodes informationrelating to a luma intra prediction mode of a prediction block of a lumasignal and information relating to a chroma intra prediction mode of aprediction block of a chroma signal based on a bitstream in which theinformation relating to the luma intra prediction mode of the predictionblock of the luma signal and the information relating to the chromaintra prediction mode of the prediction block of the chroma signallocated at a reference position that is the same as the position of theprediction block of the luma signal are continuous; and

an intra prediction unit that, when an intra prediction of the picturesignal is made in units of minimal decoding blocks set in advance, in acase where a partition mode in which the luma signal is partitionedhorizontally and vertically is set, makes an intra prediction of thechroma signal based on the decoded chroma intra prediction mode in unitsof prediction blocks of the intra prediction of the chroma signal withinthe minimal decoding block set in accordance with a chroma format.

[Item 19]

A picture decoding device that performs intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding device including:

a bitstream decoding unit that derives a partition mode in which theluma signal is partitioned horizontally and vertically when an intraprediction of a picture signal is made in units of minimal decodingblocks set in advance and decodes information relating to a luma intraprediction mode for each prediction block of the luma signal andinformation relating to a chroma intra prediction mode for eachprediction block of the chroma signal based on a bitstream in whichcoding information relating to the prediction mode is arranged;

a luma signal intra prediction unit that, in a case where the partitionmode is set, sets prediction blocks of first to fourth luma signalsacquired by partitioning the luma signal of the minimal decoding blockhorizontally and vertically and predicts the luma signal based on theneighboring blocks of decoded luma signals in accordance with each lumaintra prediction mode acquired based on the information relating to theluma intra prediction mode for each prediction block of the decoded lumasignal; and

a chroma signal intra prediction unit that, in a case where thepartition mode is set, and a chroma format is 4:4:4, sets predictionblocks of first to fourth chroma signals acquired by partitioning thechroma signal of the minimal decoding block horizontally and verticallyand predicts the chroma signal based on neighboring blocks of decodedchroma signals in accordance with each chroma intra prediction mode thatis acquired based on the information relating to the chroma intraprediction mode for each prediction block of the decoded chroma signal,

wherein the chroma signal intra prediction unit, in a case where thechroma format is 4:4:4 and a mode for setting the chroma intraprediction mode in accordance with the luma intra prediction mode isdesignated based on the information relating to the chroma intraprediction mode for each prediction block of the decoded chroma signal,sets chroma intra prediction modes of the prediction blocks of thefirst, second, third, and fourth chroma signals by using valuesrepresenting the luma intra prediction modes of the prediction blocks ofthe first, second, third, and fourth luma signals within the minimaldecoding block as values representing the chroma intra prediction modesof the prediction blocks of the first, second, third, and fourth chromasignals within the minimal decoding block that are located at respectivesame reference positions.

[Item 20]

The picture decoding device described in Item 19, wherein, in a casewhere the partition mode is derived, and the chroma format is 4:4:4, thebitstream decoding unit, based on a bitstream in which codinginformation relating to the prediction modes is arranged in order of,within the minimal decoding block, the luma intra prediction mode of theprediction block of first luma signal, the chroma intra prediction modeof the prediction block of first chroma signal located at a referenceposition that is the same as the position of the prediction block of thefirst luma signal, the luma intra prediction mode of the predictionblock of second luma signal, the chroma intra prediction mode of theprediction block of second chroma signal located at a reference positionthat is the same as the position of the prediction block of the secondluma signal, the luma intra prediction mode of the prediction block ofthird luma signal, the chroma intra prediction mode of the predictionblock of third chroma signal located at a reference position that is thesame as the position of the prediction block of the third luma signal,the luma intra prediction mode of the prediction block of fourth lumasignal, and the chroma intra prediction mode of the prediction block offourth chroma signal located at a reference position that is the same asthe position of the prediction block of the fourth luma signal, decodesthe information relating to the luma intra prediction mode of theprediction block of the luma signal and the information relating to thechroma intra prediction mode of the prediction block of the chromasignal in this order.

[Item 21]

A picture decoding device that performs intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding device including:

a bitstream decoding unit that derives a partition mode in which theluma signal is partitioned horizontally and vertically when an intraprediction of a picture signal is made in units of minimal decodingblocks set in advance and decodes information relating to a luma intraprediction mode for each prediction block of the luma signal andinformation relating to a chroma intra prediction mode for eachprediction block of the chroma signal based on a bitstream in whichcoding information relating to the prediction mode is arranged;

-   -   a luma signal intra prediction unit that, in a case where the        partition mode is set, sets prediction blocks of first to fourth        luma signals acquired by partitioning the luma signal of the        minimal decoding block horizontally and vertically and predicts        the luma signal based on neighboring blocks of decoded luma        signals in accordance with each luma intra prediction mode        acquired based on the information relating to the luma intra        prediction mode for each prediction block of the decoded luma        signal; and

a chroma signal intra prediction unit that, in a case where thepartition mode is set, and a chroma format is 4:2:2, sets predictionblocks of first and second chroma signals acquired by partitioning thechroma signal of the minimal decoding block horizontally and verticallyand predicts the chroma signal based on neighboring blocks of decodedchroma signals in accordance with each chroma intra prediction mode thatis acquired based on the information relating to the chroma intraprediction mode for each prediction block of the decoded chroma signal,

wherein the chroma signal intra prediction unit, in a case where thechroma format is 4:2:2 and a mode for setting the chroma intraprediction mode in accordance with the luma intra prediction mode isdesignated based on the information relating to the chroma intraprediction mode for each prediction block of the decoded chroma signal,sets chroma intra prediction modes of the prediction blocks of the firstand second chroma signals by converting values representing the lumaintra prediction modes of the prediction blocks of the first and thirdluma signals within the minimal decoding block into values representingthe chroma intra prediction modes of the prediction blocks of the firstand second chroma signals within the minimal decoding block that arelocated at respective same reference positions in accordance with aconversion rule set in advance.

[Item 22]

The picture decoding device described in Item 21, wherein, in a casewhere the partition mode is derived, and the chroma format is 4:2:2, thebitstream decoding unit, based on the bitstream in which the codinginformation relating to the prediction modes is arranged in order of,within the minimal decoding block, the luma intra prediction mode of theprediction block of the first luma signal, the chroma intra predictionmode of the prediction block of the first chroma signal located at areference position that is the same as the position of the predictionblock of the first luma signal, the luma intra prediction mode of theprediction block of the second luma signal, the luma intra predictionmode of the prediction block of the third luma signal, the chroma intraprediction mode of the prediction block of the second chroma signallocated at a reference position that is the same as the position of theprediction block of the third luma signal, and the luma intra predictionmode of the prediction block of the fourth luma signal, decodes theinformation relating to the luma intra prediction mode of the predictionblock of the luma signal and the information relating to the chromaintra prediction mode of the prediction block of the chroma signal inthis order.

[Item 23]

A picture decoding method for performing intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding method including, when an intra prediction of thepicture signal is made in units of coding blocks, in a case where achroma format is 4:2:2, in a mode for setting a chroma intra predictionmode in accordance with a luma intra prediction mode, setting a chromaintra prediction mode based on the luma intra prediction mode and thechroma format and making an intra prediction of the chroma signal.

[Item 24]

A picture decoding method for performing intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding method including:

consecutively decoding information relating to a luma intra predictionmode of a prediction block of a luma signal and information relating toa chroma intra prediction mode of a prediction block of a chroma signalbased on a bitstream in which the information relating to the luma intraprediction mode of the prediction block of the luma signal and theinformation relating to the chroma intra prediction mode of theprediction block of the chroma signal located at a reference positionthat is the same as the position of the prediction block of the lumasignal are continuous; and

when an intra prediction of the picture signal is made in units ofminimal decoding blocks set in advance, in a case where a partition modein which the luma signal is partitioned horizontally and vertically isset, making an intra prediction of the chroma signal based on thedecoded chroma intra prediction mode in units of prediction blocks ofthe intra prediction of the chroma signal within the minimal decodingblock set in accordance with a chroma format.

[Item 25]

A picture decoding method for performing intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding method including:

deriving a partition mode in which the luma signal is partitionedhorizontally and vertically when an intra prediction of a picture signalis made in units of minimal decoding blocks set in advance and decodinginformation relating to a luma intra prediction mode for each predictionblock of the luma signal and information relating to a chroma intraprediction mode for each prediction block of the chroma signal based ona bitstream in which coding information relating to the prediction modeis arranged;

in a case where the partition mode is set, setting prediction blocks offirst to fourth luma signals acquired by partitioning the luma signal ofthe minimal decoding block horizontally and vertically and predictingthe luma signal based on the neighboring blocks of decoded luma signalsin accordance with each luma intra prediction mode acquired based on theinformation relating to the luma intra prediction mode for eachprediction block of the decoded luma signal; and

in a case where the partition mode is set, and a chroma format is 4:4:4,setting prediction blocks of first to fourth chroma signals acquired bypartitioning the chroma signal of the minimal decoding blockhorizontally and vertically and predicting the chroma signal based onneighboring blocks of decoded chroma signals in accordance with eachchroma intra prediction mode that is acquired based on the informationrelating to the chroma intra prediction mode for each prediction blockof the decoded chroma signal,

wherein, in the setting of prediction blocks and predicting of thechroma signal, in a case where the chroma format is 4:4:4 and a mode forsetting the chroma intra prediction mode in accordance with the lumaintra prediction mode is designated based on the information relating tothe chroma intra prediction mode for each prediction block of thedecoded chroma signal, chroma intra prediction modes of predictionblocks of the first, second, third, and fourth chroma signals are set byusing values representing the luma intra prediction modes of theprediction blocks of the first, second, third, and fourth luma signalswithin the minimal decoding block as values representing the chromaintra prediction modes of the prediction blocks of the first, second,third, and fourth chroma signals within the minimal decoding block thatare located at respective same reference positions.

[Item 26]

A picture decoding method for performing intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding method including:

deriving a partition mode in which the luma signal is partitionedhorizontally and vertically when an intra prediction of a picture signalis made in units of minimal decoding blocks set in advance and decodinginformation relating to a luma intra prediction mode for each predictionblock of the luma signal and information relating to a chroma intraprediction mode for each prediction block of the chroma signal based ona bitstream in which coding information relating to the prediction modeis arranged;

in a case where the partition mode is set, setting prediction blocks offirst to fourth luma signals acquired by partitioning the luma signal ofthe minimal decoding block horizontally and vertically and predictingthe luma signal based on neighboring blocks of decoded luma signals inaccordance with each luma intra prediction mode acquired based on theinformation relating to the luma intra prediction mode for eachprediction block of the decoded luma signal; and

in a case where the partition mode is set, and a chroma format is 4:2:2,setting prediction blocks of first and second chroma signals acquired bypartitioning the chroma signal of the minimal decoding blockhorizontally and vertically and predicting the chroma signal based onneighboring blocks of decoded chroma signals in accordance with eachchroma intra prediction mode that is acquired based on the informationrelating to the chroma intra prediction mode for each prediction blockof the decoded chroma signal,

wherein, in the setting of prediction blocks and predicting of thechroma signal, in a case where the chroma format is 4:2:2 and a mode forsetting the chroma intra prediction mode in accordance with the lumaintra prediction mode is designated based on the information relating tothe chroma intra prediction mode for each prediction block of thedecoded chroma signal, chroma intra prediction modes of the predictionblocks of the first and second chroma signals are set by convertingvalues representing the luma intra prediction modes of the predictionblocks of the first and third luma signals within the minimal decodingblock into values representing the chroma intra prediction modes of theprediction blocks of the first and second chroma signals within theminimal decoding block that are located at respective same referencepositions in accordance with a conversion rule set in advance.

[Item 27]

A picture decoding program for performing intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding program causing a computer to execute, when an intraprediction of the picture signal is made in units of coding blocks, in acase where a chroma format is 4:2:2, in a mode for setting a chromaintra prediction mode in accordance with a luma intra prediction mode,setting a chroma intra prediction mode based on the luma intraprediction mode and the chroma format and making an intra prediction ofthe chroma signal.

[Item 28]

A picture decoding program for performing intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding program causing a computer to execute:

consecutively decoding information relating to a luma intra predictionmode of a prediction block of a luma signal and information relating toa chroma intra prediction mode of a prediction block of a chroma signalbased on a bitstream in which the information relating to the luma intraprediction mode of the prediction block of the luma signal and theinformation relating to the chroma intra prediction mode of theprediction block of the chroma signal located at a reference positionthat is the same as the position of the prediction block of the lumasignal are continuous; and

when an intra prediction of the picture signal is made in units ofminimal decoding blocks set in advance, in a case where a partition modein which the luma signal is partitioned horizontally and vertically isset, making an intra prediction of the chroma signal based on thedecoded chroma intra prediction mode in units of prediction blocks ofthe intra prediction of the chroma signal within the minimal decodingblock set in accordance with a chroma format.

[Item 29]

A picture decoding program for performing intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding program causing a computer to execute:

deriving a partition mode in which the luma signal is partitionedhorizontally and vertically when an intra prediction of a picture signalis made in units of minimal decoding blocks set in advance and decodinginformation relating to a luma intra prediction mode for each predictionblock of the luma signal and information relating to a chroma intraprediction mode for each prediction block of the chroma signal based ona bitstream in which coding information relating to the prediction modeis arranged;

in a case where the partition mode is set, setting prediction blocks offirst to fourth luma signals acquired by partitioning the luma signal ofthe minimal decoding block horizontally and vertically and predictingthe luma signal based on the neighboring blocks of decoded luma signalsin accordance with each luma intra prediction mode acquired based on theinformation relating to the luma intra prediction mode for eachprediction block of the decoded luma signal; and

in a case where the partition mode is set, and a chroma format is 4:4:4,setting prediction blocks of first to fourth chroma signals acquired bypartitioning the chroma signal of the minimal decoding block andpredicting the chroma signal based on neighboring blocks of decodedchroma signals in accordance with each chroma intra prediction mode thatis acquired based on the information relating to the chroma intraprediction mode for each prediction block of the decoded chroma signal,

wherein, in the setting of prediction blocks and predicting of thechroma signal, in a case where the chroma format is 4:4:4 and a mode forsetting the chroma intra prediction mode in accordance with the lumaintra prediction mode is designated based on the information relating tothe chroma intra prediction mode for each prediction block of thedecoded chroma signal, chroma intra prediction modes of the predictionblocks of the first, second, third, and fourth chroma signals are set byusing values representing the luma intra prediction modes of theprediction blocks of the first, second, third, and fourth luma signalswithin the minimal decoding block as values representing the chromaintra prediction modes of the prediction blocks of the first, second,third, and fourth chroma signals within the minimal decoding block thatare located at respective same reference positions.

[Item 30]

A picture decoding program for performing intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding program causing a computer to execute:

deriving a partition mode in which the luma signal is partitionedhorizontally and vertically when an intra prediction of a picture signalis made in units of minimal decoding blocks set in advance and decodinginformation relating to a luma intra prediction mode for each predictionblock of the luma signal and information relating to a chroma intraprediction mode for each prediction block of the chroma signal based ona bitstream in which coding information relating to the prediction modeis arranged;

in a case where the partition mode is set, setting prediction blocks offirst to fourth luma signals acquired by partitioning the luma signal ofthe minimal decoding block horizontally and vertically and predictingthe luma signal based on neighboring blocks of decoded luma signals inaccordance with each luma intra prediction mode acquired based on theinformation relating to the luma intra prediction mode for eachprediction block of the decoded luma signal; and

in a case where the partition mode is set, and a chroma format is 4:2:2,setting prediction blocks of first and second chroma signals acquired bypartitioning the chroma signal of the minimal decoding blockhorizontally and vertically and predicting the chroma signal based onneighboring blocks of decoded chroma signals in accordance with eachchroma intra prediction mode that is acquired based on the informationrelating to the chroma intra prediction mode for each prediction blockof the decoded chroma signal,

wherein, in the setting of prediction blocks and predicting of thechroma signal, in a case where the chroma format is 4:2:2 and a mode forsetting the chroma intra prediction mode in accordance with the lumaintra prediction mode is designated based on the information relating tothe chroma intra prediction mode for each prediction block of thedecoded chroma signal, chroma intra prediction modes of the first andsecond chroma signals are set by converting values representing the lumaintra prediction modes of the prediction blocks of the first and thirdluma signals within the minimal decoding block into values representingthe chroma intra prediction modes of the prediction blocks of the firstand second chroma signals within the minimal decoding block that arelocated at respective same reference positions in accordance with aconversion rule set in advance.

[Item 31]

A picture decoding device that performs intra prediction decoding of apicture signal including a luma signal and a chroma signal in units ofblocks by decoding information relating to an intra prediction mode, thepicture decoding device including:

a luma intra prediction mode derivation unit that derives a value of aluma intra prediction mode; and

an intra prediction mode derivation unit that derives a value of achroma intra prediction mode from a conversion table representing avalue of the chroma intra prediction mode having a chroma format of4:2:2 based on a value of the luma intra prediction mode of a predictionblock located at a same position as the position of a prediction blockof the chroma signal, which is derived by the luma intra prediction modederivation unit, in a case where the chroma format is 4:2:2 and derivesa value of the chroma intra prediction mode based on a value of the lumaintra prediction mode of a prediction block located at a same positionas the position of a prediction block of the chroma signal without usingthe conversion table in a case where the chroma format is not 4:2:2.

[Item 32]

The picture decoding device described in Item 31, wherein, in theconversion table, at least values representing a plurality of chromaintra prediction modes in prediction directions that are respectivelyclosest to a plurality of directions derived by scaling ½ times ofprediction directions of a plurality of luma intra prediction modes inwhich reference destinations are aligned in a horizontal direction inthe horizontal direction.

What is claimed is:
 1. A picture decoding device that performs intraprediction decoding of a picture signal including a luma signal and achroma signal in units of blocks by decoding information relating to anintra prediction mode, the picture decoding device comprising: a lumaintra prediction mode derivation unit that is configured to derive avalue of a luma intra prediction mode; and an intra prediction modederivation unit that is configured to derive a value of a chroma intraprediction mode from a conversion table representing a value of thechroma intra prediction mode having a chroma format of 4:2:2 based on avalue of the luma intra prediction mode of a prediction block located ata same position as the position of a prediction block of the chromasignal, which is derived by the luma intra prediction mode derivationunit, in a case where the chroma format is 4:2:2 and derive a value ofthe chroma intra prediction mode based on a value of the luma intraprediction mode of a prediction block located at a same position as theposition of a prediction block of the chroma signal without using theconversion table in a case where the chroma format is not 4:2:2, whereinthe conversion table shows at least values representing a plurality ofchroma intra prediction modes having prediction directions that arerespectively closest to a plurality of directions derived by performing½ times scaling horizontally for prediction directions of a plurality ofthe luma intra prediction modes in which reference destinations arehorizontally aligned and the conversion table shows a same unalteredvalue as a value representing the chroma intra prediction mode as to avalue representing the luma intra prediction mode of vertical predictionin which a prediction direction is a vertical direction.
 2. A picturedecoding method for performing intra prediction decoding of a picturesignal including a luma signal and a chroma signal in units of blocks bydecoding information relating to an intra prediction mode, the picturedecoding method comprising: deriving a value of a luma intra predictionmode; and deriving a value of a chroma intra prediction mode from aconversion table representing a value of the chroma intra predictionmode having a chroma format of 4:2:2 based on a value of the luma intraprediction mode of a prediction block located at a same position as theposition of a prediction block of the chroma signal, which is derived inthe deriving of a value of the luma intra prediction mode, in a casewhere the chroma format is 4:2:2 and deriving a value of the chromaintra prediction mode based on a value of the luma intra prediction modeof a prediction block located at a same position as the position of aprediction block of the chroma signal without using the conversion tablein a case where the chroma format is not 4:2:2, wherein the conversiontable shows at least values representing a plurality of chroma intraprediction modes having prediction directions that are respectivelyclosest to a plurality of directions derived by performing ½ timesscaling horizontally for prediction directions of a plurality of theluma intra prediction modes in which reference destinations arehorizontally aligned and the conversion table shows a same unalteredvalue as a value representing the chroma intra prediction mode as to avalue representing the luma intra prediction mode of vertical predictionin which a prediction direction is a vertical direction.
 3. A recordingmedium in which a picture decoding program causing a computer to executeperforming intra prediction decoding of a picture signal including aluma signal and a chroma signal in units of blocks by decodinginformation relating to an intra prediction mode is stored, the picturedecoding program causing the computer to execute: deriving a value of aluma intra prediction mode; and deriving a value of a chroma intraprediction mode from a conversion table representing a value of thechroma intra prediction mode having a chroma format of 4:2:2 based on avalue of the luma intra prediction mode of a prediction block located ata same position as the position of a prediction block of the chromasignal, which is derived in the deriving of a value of the luma intraprediction mode, in a case where the chroma format is 4:2:2 and derivinga value of the chroma intra prediction mode based on a value of the lumaintra prediction mode of a prediction block located at a same positionas the position of a prediction block of the chroma signal without usingthe conversion table in a case where the chroma format is not 4:2:2,wherein the conversion table shows at least values representing aplurality of chroma intra prediction modes having prediction directionsthat are respectively closest to a plurality of directions derived byperforming ½ times scaling horizontally for prediction directions of aplurality of the luma intra prediction modes in which referencedestinations are horizontally aligned and the conversion table shows asame unaltered value as a value representing the chroma intra predictionmode as to a value representing the luma intra prediction mode ofvertical prediction in which a prediction direction is a verticaldirection.